ACT Math : Geometry

Study concepts, example questions & explanations for ACT Math

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #11 : How To Find The Angle Of Clock Hands

What is the angle of the minor arc between the minute and hour hands of a clock reading \displaystyle 11\textup{:}39? Assume a \displaystyle \textup{12-hour} display (not a military clock).

Possible Answers:

\displaystyle \left (\frac{231}{2} \right )^{\circ}

\displaystyle \left (\frac{699}{2}} \right )^{\circ}

\displaystyle 35^{\circ}

\displaystyle \left (\frac{329}{2} \right )^{\circ}

\displaystyle 28^{\circ}

Correct answer:

\displaystyle \left (\frac{231}{2} \right )^{\circ}

Explanation:

To find angular distance between the minute and hour hand, first find the position of each. Using \displaystyle 12\textup{:}00 as a reference (both hands straight up), we can calculate the difference in degree more easily.

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

For the hour hand, each hour in a 12-hour cycle takes up \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} of angular distance, which means each minute takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of distance for the hour hand.

Thus, our distance from \displaystyle 12:00 (our reference angle) in degrees for the minute hand can be expressed as \displaystyle d(M) = (6m)^{\circ}, where \displaystyle m is the number of minutes that have passed.

Likewise, our distance from \displaystyle 12:00 in degrees for the hour hand can be expressed as \displaystyle d(H) = (\frac{m}{2})^{\circ}, where \displaystyle m is again the number of minutes that have passed.

Then, all we need to do is find the positive difference between these two measurements, \displaystyle \left | d(M) -d(H) \right |, and we have our angle.

This looks more complicated than it is! Fortunately, once our equation is set up, the problem is as easy as plug and play. First, let's find the measure of the minor arc between the minute hand and the reference. We can ignore hours (as each hour returns the minute hand to our reference angle) and just look at minutes.

\displaystyle d(M) = (6m)^{\circ} = (6\cdot39)^{\circ} = 234^{\circ}

Now, find the same distance, but for the hour hand. Here, we must consider both hours and minutes by using a fraction:

\displaystyle d(H) = (\frac{m}{2})^{\circ} = (\frac{(11\cdot60)+39}{2})^{\circ} = (\frac{699}{2})^{\circ}

Lastly, we find the difference between these two references (remembering that our answer should be positive):

\displaystyle \left | d(M) -d(H) \right | = \left \| 234^{\circ} - (\frac{699}{2})^{\circ} \right \| = (\frac{231}{2})^{\circ}

Thus, the hands are \displaystyle (\frac{231}{2})^{\circ} apart at \displaystyle 11:39.

Example Question #491 : Geometry

What is the angle of the minor arc between the minute and hour hands of a clock reading \displaystyle 4\textup{:}40? Assume a \displaystyle \textup{12-hour} display (not a military clock).

Possible Answers:

\displaystyle \left (\frac{317}{2} \right )^{\circ}

\displaystyle 120^{\circ}

\displaystyle 100^{\circ}

\displaystyle \left (\frac{211}{2} \right )^{\circ}

\displaystyle 210^{\circ}

Correct answer:

\displaystyle 100^{\circ}

Explanation:

To find angular distance between the minute and hour hand, first find the position of each. Using \displaystyle 12\textup{:}00 as a reference (both hands straight up), we can calculate the difference in degree more easily.

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

For the hour hand, each hour in a 12-hour cycle takes up \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} of angular distance, which means each minute takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of distance for the hour hand.

Thus, our distance from \displaystyle 12:00 (our reference angle) in degrees for the minute hand can be expressed as \displaystyle d(M) = (6m)^{\circ}, where \displaystyle m is the number of minutes that have passed.

Likewise, our distance from \displaystyle 12:00 in degrees for the hour hand can be expressed as \displaystyle d(H) = (\frac{m}{2})^{\circ}, where \displaystyle m is again the number of minutes that have passed.

Then, all we need to do is find the positive difference between these two measurements, \displaystyle \left | d(M) -d(H) \right |, and we have our angle.

This looks more complicated than it is! Fortunately, once our equation is set up, the problem is as easy as plug and play. First, let's find the measure of the minor arc between the minute hand and the reference. We can ignore hours (as each hour returns the minute hand to our reference angle) and just look at minutes.

\displaystyle d(M) = (6m)^{\circ} = (6\cdot40)^{\circ} = 240^{\circ}

Now, find the same distance, but for the hour hand. Here, we must consider both hours and minutes by using a fraction:

\displaystyle d(H) = (\frac{m}{2})^{\circ} = (\frac{(4\cdot60)+40}{2})^{\circ} = (\frac{280}{2})^{\circ} = 140^{\circ}

Lastly, we find the difference between these two references (remembering that our answer should be positive):

\displaystyle \left | d(M) -d(H) \right | = \left \| 240^{\circ} - 140^{\circ} \right \| = 100^{\circ}

Thus, the hands are \displaystyle 100^{\circ} apart at \displaystyle 4:40.

Example Question #12 : How To Find The Angle Of Clock Hands

What is the angle of the major arc between the minute and hour hands of a clock reading \displaystyle 6\textup{:}02? Assume a \displaystyle \textup{12-hour} display (not a military clock).

Possible Answers:

\displaystyle 123^{\circ}

\displaystyle 241^{\circ}

\displaystyle 288^{\circ}

\displaystyle 222^{\circ}

\displaystyle 191^{\circ}

Correct answer:

\displaystyle 191^{\circ}

Explanation:

To find angular distance between the minute and hour hand, first find the position of each. Using \displaystyle 12\textup{:}00 as a reference (both hands straight up), we can calculate the difference in degree more easily.

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

For the hour hand, each hour in a 12-hour cycle takes up \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} of angular distance, which means each minute takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of distance for the hour hand.

Thus, our distance from \displaystyle 12:00 (our reference angle) in degrees for the minute hand can be expressed as \displaystyle d(M) = (6m)^{\circ}, where \displaystyle m is the number of minutes that have passed.

Likewise, our distance from \displaystyle 12:00 in degrees for the hour hand can be expressed as \displaystyle d(H) = (\frac{m}{2})^{\circ}, where \displaystyle m is again the number of minutes that have passed.

Then, all we need to do is find the positive difference between these two measurements, \displaystyle \left | d(M) -d(H) \right |, and we have our angle.

This looks more complicated than it is! Fortunately, once our equation is set up, the problem is as easy as plug and play. First, let's find the measure of the minor arc between the minute hand and the reference. We can ignore hours (as each hour returns the minute hand to our reference angle) and just look at minutes.

\displaystyle d(M) = (6m)^{\circ} = (6\cdot2)^{\circ} = 12^{\circ}

Now, find the same distance, but for the hour hand. Here, we must consider both hours and minutes by using a fraction:

\displaystyle d(H) = (\frac{m}{2})^{\circ} = (\frac{(6\cdot60)+2}{2})^{\circ} = (\frac{362}{2})^{\circ} = 181^{\circ}

Lastly, we find the difference between these two references (remembering that our answer should be positive):

\displaystyle \left | d(M) -d(H) \right | = \left \| 181^{\circ} - 12^{\circ} \right \| = 169^{\circ}

The problem asked for the major arc, so our answer is actually \displaystyle 360-169= 191^{\circ}

Thus, the hands are \displaystyle 191^{\circ} apart at \displaystyle 6\textup{:}02.

Example Question #12 : How To Find The Angle Of Clock Hands

What is the angle of the major arc between the minute and hour hands of a clock reading \displaystyle 11\textup{:}05? Assume a \displaystyle \textup{12-hour} display (not a military clock).

Possible Answers:

\displaystyle 199^{\circ}

\displaystyle 278^{\circ}

\displaystyle \left (233\frac{1}{2} \right )^{\circ}

\displaystyle 320^{\circ}

\displaystyle \left (302\frac{1}{2} \right )^{\circ}

Correct answer:

\displaystyle \left (302\frac{1}{2} \right )^{\circ}

Explanation:

To find angular distance between the minute and hour hand, first find the position of each. Using \displaystyle 12:00 as a reference (both hands straight up), we can calculate the difference in degree more easily.

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

For the hour hand, each hour in a 12-hour cycle takes up \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} of angular distance, which means each minute takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of distance for the hour hand.

Thus, our distance from \displaystyle 12:00 (our reference angle) in degrees for the minute hand can be expressed as \displaystyle d(M) = (6m)^{\circ}, where \displaystyle m is the number of minutes that have passed.

Likewise, our distance from \displaystyle 12:00 in degrees for the hour hand can be expressed as \displaystyle d(H) = (\frac{m}{2})^{\circ}, where \displaystyle m is again the number of minutes that have passed.

Then, all we need to do is find the positive difference between these two measurements, \displaystyle \left | d(M) -d(H) \right |, and we have our angle.

This looks more complicated than it is! Fortunately, once our equation is set up, the problem is as easy as plug and play. First, let's find the measure of the minor arc between the minute hand and the reference. We can ignore hours (as each hour returns the minute hand to our reference angle) and just look at minutes.

\displaystyle d(M) = (6m)^{\circ} = (6\cdot5)^{\circ} = 30^{\circ}

Now, find the same distance, but for the hour hand. Here, we must consider both hours and minutes by using a fraction:

\displaystyle d(H) = (\frac{m}{2})^{\circ} = (\frac{(11\cdot60)+5}{2})^{\circ} = (\frac{665}{2})^{\circ} = (332 \frac{1}{2})^{\circ}

Lastly, we find the difference between these two references (remembering that our answer should be positive):

\displaystyle \left | d(M) -d(H) \right | = \left \| 30^{\circ} - (332\frac{1}{2})^{\circ} \right \| = (302\frac{1}{2})^{\circ}

Thus, the hands are \displaystyle (302\frac{1}{2})^{\circ} apart at \displaystyle 11:05.

Example Question #13 : How To Find The Angle Of Clock Hands

What is the angle of the major arc between the minute and hour hands of a clock reading \displaystyle 4\textup{:}14? Assume ab\displaystyle \textup{12-hour} display (not a military clock).

Possible Answers:

\displaystyle 305^{\circ}

\displaystyle 27^{\circ}

\displaystyle 333^{\circ}

\displaystyle 317^{\circ}

\displaystyle 43^{\circ}

Correct answer:

\displaystyle 317^{\circ}

Explanation:

To find angular distance between the minute and hour hand, first find the position of each. Using \displaystyle 12:00 as a reference (both hands straight up), we can calculate the difference in degree more easily.

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

For the hour hand, each hour in a 12-hour cycle takes up \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} of angular distance, which means each minute takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of distance for the hour hand.

Thus, our distance from \displaystyle 12:00 (our reference angle) in degrees for the minute hand can be expressed as \displaystyle d(M) = (6m)^{\circ}, where \displaystyle m is the number of minutes that have passed.

Likewise, our distance from \displaystyle 12:00 in degrees for the hour hand can be expressed as \displaystyle d(H) = (\frac{m}{2})^{\circ}, where \displaystyle m is again the number of minutes that have passed.

Then, all we need to do is find the positive difference between these two measurements, \displaystyle \left | d(M) -d(H) \right |, and we have our angle.

This looks more complicated than it is! Fortunately, once our equation is set up, the problem is as easy as plug and play. First, let's find the measure of the minor arc between the minute hand and the reference. We can ignore hours (as each hour returns the minute hand to our reference angle) and just look at minutes.

\displaystyle d(M) = (6m)^{\circ} = (6\cdot14)^{\circ} = 84^{\circ}

Now, find the same distance, but for the hour hand. Here, we must consider both hours and minutes by using a fraction:

\displaystyle d(H) = (\frac{m}{2})^{\circ} = (\frac{(4\cdot60)+14}{2})^{\circ} = (\frac{254}{2})^{\circ} = 127^{\circ}

Lastly, we find the difference between these two references (remembering that our answer should be positive):

\displaystyle \left | d(M) -d(H) \right | = \left \| 84^{\circ} - 127^{\circ} \right \| = 43^{\circ}

The problem asked for the major arc, so our answer is actually \displaystyle 360-43= 317^{\circ}

Thus, the hands are \displaystyle 317^{\circ} apart at \displaystyle 4:14.

Example Question #13 : How To Find The Angle Of Clock Hands

A watch's hands move from \displaystyle 3\textup{:}30 to \displaystyle 5\textup{:}25. What total angular distance does the minute hand move?

Possible Answers:

\displaystyle 370^{\circ}

\displaystyle 555^{\circ}

\displaystyle 30^{\circ}

\displaystyle 225^{\circ}

\displaystyle 690^{\circ}

Correct answer:

\displaystyle 690^{\circ}

Explanation:

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

Thus, our total distance from our reference angle can be found as \displaystyle d(m) = 6m^{\circ}, where \displaystyle m is the number of minutes that have elapsed.

In this case, we simply find the difference of the two times, remembering to first convert hours to minutes:

\displaystyle 5:25-3:30 = 325 -210 = 115

Now, plug our answer in minutes into our equation:

 \displaystyle d(m) = 6m^{\circ} = 6(115)^{\circ} = 690^{\circ}

So, our minute hand has moved \displaystyle 690^{\circ} in total.

Example Question #14 : How To Find The Angle Of Clock Hands

A watch's hands move from \displaystyle 5\textup{:}17 to \displaystyle 11\textup{:}19. What total angular distance does the minute hand move?

Possible Answers:

\displaystyle 2465^{\circ}

\displaystyle 2336^{\circ}

\displaystyle 2172^{\circ}

\displaystyle 1833^{\circ}

\displaystyle 3020^{\circ}

Correct answer:

\displaystyle 2172^{\circ}

Explanation:

First, remember that a circle contains \displaystyle 360^{\circ}, and therefore for the minute hand, each minute past the hour takes up \displaystyle \frac{360^{\circ}}{60} = 6^{\circ} of angular distance.

Thus, our total distance from our reference angle can be found as \displaystyle d(m) = 6m^{\circ}, where \displaystyle m is the number of minutes that have elapsed.

In this case, we simply find the difference of the two times, remembering to first convert hours to minutes:

\displaystyle 11\textup{:}19-5\textup{:}17 = 679 -317 = 362

Now, plug our answer in minutes into our equation:

 \displaystyle d(m) = 6m^{\circ} = 6(362)^{\circ} = 2172^{\circ}

So, our minute hand has moved \displaystyle 2172^{\circ} in total.

Example Question #13 : How To Find The Angle Of Clock Hands

A watch's hands move from \displaystyle 4\textup{:}10 to \displaystyle 8\textup{:}38. What total angular distance does the minute hand move?

Possible Answers:

\displaystyle 1094^{\circ}

\displaystyle 134^{\circ}

\displaystyle 868^{\circ}

\displaystyle 248^{\circ}

\displaystyle 89^{\circ}

Correct answer:

\displaystyle 134^{\circ}

Explanation:

First, remember that an hour hand moves \displaystyle \frac{360^{\circ}}{12} = 30^{\circ} for each hour that passes, and therefore for the hour hand, each minute past the hour takes up \displaystyle \frac{30^{\circ}}{60} = (\frac{1}{2})^{\circ} of angular distance.

Thus, our total distance from our reference angle can be found as \displaystyle d(h) = (\frac{m}{2})^{\circ}, where \displaystyle m is the number of minutes that have elapsed.

In this case, we simply find the difference of the two times, remembering to first convert hours to minutes:

\displaystyle 8\textup{:}38-4\textup{:}10 = 518 -250 = 268

Now, plug our answer in minutes into our equation:

 \displaystyle d(h) = (\frac{m}{2})^{\circ} = (\frac{268}{2})^{\circ} = 134^{\circ}

So, our hour hand has moved \displaystyle 134^{\circ} in total.

Example Question #21 : Circles

A clock reads \displaystyle 3:00 pm.  What is the angle formed between the minute and hour hand on the clock?

Possible Answers:

\displaystyle 90\; degrees

\displaystyle 120 \; degrees

\displaystyle 60\;degrees

\displaystyle 180 \;degrees

\displaystyle 30\;degrees

Correct answer:

\displaystyle 90\; degrees

Explanation:

When the clock reads \displaystyle 3:00, the hour hand is on the \displaystyle 3, and the minute hand is on the \displaystyle 12.  If we think about this as a fraction, there are twelve spots the hour hand can be on, which we means we are on the \displaystyle \frac{3}{12} position.  

Since there are \displaystyle 360 \; degrees in a circle, the angle can simply be found by multiplying this fraction by the number of degrees in a circle:

\displaystyle \frac{3}{12}*360\;degrees=90\;degrees

Alternatively, if the clock reads \displaystyle 3:00, the angle the clock reads is visually \displaystyle \frac{1}{4} of the entire clock, which has \displaystyle 360\;degrees.

  \displaystyle \frac{1}{4}*360\;degrees=90\;degrees.

Example Question #21 : How To Find The Angle Of Clock Hands

On a standard analog clock, what is the angle between the hands when the clock reads \displaystyle \textup{11:20}? Give the smaller of the two angles.

Possible Answers:

\displaystyle 280^{\circ}

\displaystyle 90^{\circ}

\displaystyle 85^{\circ}

\displaystyle 140^{\circ}

\displaystyle 125^{\circ}

Correct answer:

\displaystyle 140^{\circ}

Explanation:

To find the degrees of a clock hand, first find the angle between each hour-long sections. Since there are \displaystyle 12 evenly spaced sections, we find that each section has an angle of: \displaystyle 360$^{\circ}$/12=30$^{\circ}$. at \displaystyle \textup{11:20} the hour hand has gone one-third of the way between the \displaystyle 11and \displaystyle 12. Thus there are two-thirds of \displaystyle 30^{\circ} between the hour hand and the \displaystyle 12. \displaystyle \left (\frac{2}{3} \right )*30^{\circ} = 20^{\circ}.

 

There are \displaystyle 120^{\circ} between \displaystyle 12 and \displaystyle 4, where the minute hands is. Thus there's a total of \displaystyle 20^{\circ} + 120^{\circ} = 140^{\circ} between the hands.

Learning Tools by Varsity Tutors