ISEE Lower Level Math : Probability

Study concepts, example questions & explanations for ISEE Lower Level Math

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Example Questions

Example Question #81 : How To Find The Probability Of An Outcome

If a class has 10 boys and 12 girls, what is the probability the teacher will call on a boy?

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle \frac{1}{10}\)

\(\displaystyle \frac{5}{11}\)

\(\displaystyle 10\)

\(\displaystyle \frac{10}{12}\)

Correct answer:

\(\displaystyle \frac{5}{11}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of an event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, in the event of calling on a boy in the class, we can determine the number of ways the event can happen:

\(\displaystyle \text{number of ways event can happen} = 10\)

because there are 10 boy students in the class.

 

To find the number of possible outcomes, we get

\(\displaystyle \text{total number of possible outcomes} = 22\)

because there are 22 total students the teacher could potentially call on.

 

Knowing all of this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of calling on a boy} = \frac{10}{22}\)

\(\displaystyle \text{probability of calling on a boy} = \frac{5}{11}\)

 

Therefore, the probability of calling on a boy is \(\displaystyle \frac{5}{11}\).

Example Question #82 : How To Find The Probability Of An Outcome

If a class has 10 boys and 12 girls, what is the probability the teacher will call on a girl?

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle \frac{12}{10}\)

\(\displaystyle \frac{6}{11}\)

\(\displaystyle 10\)

\(\displaystyle \frac{1}{12}\)

Correct answer:

\(\displaystyle \frac{6}{11}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of an event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, in the event of calling on a girl in the class, we can determine the number of ways the event can happen:

\(\displaystyle \text{number of ways event can happen} = 12\)

because there are 12 girl students in the class.

 

To find the number of possible outcomes, we get

\(\displaystyle \text{total number of possible outcomes} = 22\)

because there are 22 total students the teacher could potentially call on.

 

Knowing all of this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of calling on a girl} = \frac{12}{22}\)

\(\displaystyle \text{probability of calling on a girl} = \frac{6}{11}\)

 

Therefore, the probability of calling on a girl is \(\displaystyle \frac{6}{11}\).

Example Question #81 : How To Find The Probability Of An Outcome

A box contains the following:

  • 2 red marbles
  • 1 blue marbles
  • 3 green marbles

What is the probability of picking a green marble?

Possible Answers:

\(\displaystyle \frac{1}{3}\)

\(\displaystyle 3\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{2}{3}\)

\(\displaystyle \frac{3}{4}\)

Correct answer:

\(\displaystyle \frac{1}{2}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, given the event of drawing a green marble, we can calculate the following.

\(\displaystyle \text{number of ways event can happen} = 3\)

because there are 3 green marbles that we can pick.

 

Now, we can calculate the following.

\(\displaystyle \text{total number of possible outcomes} = 6\)

because there are 6 total different marbles we could potentially pick.

 

Knowing this, we can substitute into the formula.

\(\displaystyle \text{probability of picking a green marble} = \frac{3}{6}\)

\(\displaystyle \text{probability of picking a green marble} = \frac{1}{2}\)

 

Therefore, the probability of picking a green marble from the box is \(\displaystyle \frac{1}{2}\).

Example Question #81 : How To Find The Probability Of An Outcome

There are 10 bottles of water and 8 bottles of juice in the refrigerator. 

What is the probability of grabbing a bottle of water?

Possible Answers:

\(\displaystyle \frac{1}{10}\)

\(\displaystyle \frac{2}{10}\)

\(\displaystyle \frac{10}{8}\)

\(\displaystyle 10\)

\(\displaystyle \frac{5}{9}\)

Correct answer:

\(\displaystyle \frac{5}{9}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, given the event of grabbing a bottle of water, we can calculate the following.

\(\displaystyle \text{number of ways event can happen} = 10\)

because there are 10 bottles of water we can grab.

Now, we can calculate the following.

\(\displaystyle \text{total number of possible outcomes} = 18\)

because there are 18 total bottles in the refrigerator (10 water + 8 juice = 18 total).

 

Knowing this, we can substitute into the formula.

\(\displaystyle \text{probability of grabbing a bottle of water} = \frac{10}{18}\)

\(\displaystyle \text{probability of grabbing a bottle of water} = \frac{5}{9}\)

 

Therefore, the probability of picking a green marble from the box is \(\displaystyle \frac{5}{9}\).

Example Question #83 : How To Find The Probability Of An Outcome

A classroom contains the following students:

  • 10 girls
  • 13 boys

Find the probability the teacher calls on a girl.

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle \frac{10}{13}\)

\(\displaystyle 13\)

\(\displaystyle \frac{10}{23}\)

\(\displaystyle \frac{1}{10}\)

Correct answer:

\(\displaystyle \frac{10}{23}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, given the event of the teacher calling on a girl, we can calculate the following:

\(\displaystyle \text{number of ways event can happen} = 10\)

because there are 10 girls in the classroom.

 

Now, we can calculate the following:

\(\displaystyle \text{total number of possible outcomes} = 23\)

because there are 23 total students the teacher could potentially call on:

  • 10 girls
  • 13 boys

\(\displaystyle 10+13=23\)

 

Knowing this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of calling on a girl} = \frac{10}{23}\)

 

Therefore, the probability of the teacher calling on a girl is \(\displaystyle \frac{10}{23}\)

Example Question #84 : How To Find The Probability Of An Outcome

A bag contains the following:

  • 2 red pens
  • 3 blue pens
  • 2 black pens

What is the probability of grabbing a black pen from the bag?

Possible Answers:

\(\displaystyle \frac{2}{5}\)

\(\displaystyle 2\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{3}{7}\)

\(\displaystyle \frac{2}{7}\)

Correct answer:

\(\displaystyle \frac{2}{7}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Now, given the event of grabbing a black pen from the bag, we can calculate the following:

\(\displaystyle \text{number of ways event can happen} = 2\)

because there are 2 black pens in the bag.

 

Now, we can calculate the following:

\(\displaystyle \text{total number of possible outcomes} = 7\)

because there are 7 objects in the bag we could potentially grab:

  • 2 red pens
  • 3 blue pens
  • 2 black pens

\(\displaystyle 2+3+2=7\)

 

Knowing this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of grabbing a black pen} = \frac{2}{7}\)

 

Therefore, the probability of grabbing a black pen from the bag is \(\displaystyle \frac{2}{7}\).

Example Question #621 : Isee Lower Level (Grades 5 6) Mathematics Achievement

A bag contains the following:

  • 3 blue pens
  • 5 black pens
  • 7 red pens

Find the probability of drawing a black pen from the bag.

Possible Answers:

\(\displaystyle 5\)

\(\displaystyle \frac{1}{15}\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{1}{5}\)

\(\displaystyle \frac{5}{10}\)

Correct answer:

\(\displaystyle \frac{1}{3}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

So, given the event of drawing a black pen from a bag, we can calculate the following:

\(\displaystyle \text{number of ways event can happen} = 5\)

because there are 5 black pens in the bag we can choose from.

 

Now, we can calculate the following:

\(\displaystyle \text{total number of possible outcomes} = 15\)

because there are 15 total objects in the bag we could potentially draw:

  • 3 blue pens
  • 5 black pens
  • 7 red pens

\(\displaystyle 3+5+7=15\)

 

Knowing this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of drawing black pen} = \frac{5}{15}\)

\(\displaystyle \text{probability of drawing black pen} = \frac{1}{3}\)

 

Therefore, the probability of drawing a black pen from a bag is \(\displaystyle \frac{1}{3}\).

Example Question #81 : How To Find The Probability Of An Outcome

A classroom contains the following:

  • 6 black chairs
  • 7 blue chairs
  • 2 red chairs

Find the probability you will sit in a red chair.

Possible Answers:

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{2}{15}\)

\(\displaystyle \frac{2}{13}\)

\(\displaystyle 2\)

\(\displaystyle \frac{1}{15}\)

Correct answer:

\(\displaystyle \frac{2}{15}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

So, given the event of sitting in a red chair, we can calculate the following:

\(\displaystyle \text{number of ways event can happen} = 2\)

because there are 2 red chairs in the classroom.

 

Now, we can calculate the following:

\(\displaystyle \text{total number of possible outcomes} = 15\)

because there are 15 different chairs we could potentially sit on.

  • 6 black chairs
  • 7 blue chairs
  • 2 red chairs

\(\displaystyle 6+7+2=15\)

 

Knowing this, we can substitute into the formula.  We get

\(\displaystyle \text{probability of sitting in a red chair} = \frac{2}{15}\)

 

Therefore, the probability of sitting in a red chair is \(\displaystyle \frac{2}{15}\).

Example Question #85 : How To Find The Probability Of An Outcome

A bag contains the following:

  • 3 red pens
  • 5 blue pens
  • 6 black pens

Find the probability of grabbing a blue pen from the bag.

Possible Answers:

\(\displaystyle \frac{5}{14}\)

\(\displaystyle \frac{1}{14}\)

\(\displaystyle 5\)

\(\displaystyle \frac{1}{5}\)

\(\displaystyle \frac{1}{9}\)

Correct answer:

\(\displaystyle \frac{5}{14}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

Given the event of grabbing a blue pen from the bag, we can determine

\(\displaystyle \text{number of ways event can happen} = 5\)

because there are 5 blue pens in the bag. 

 

\(\displaystyle \text{total number of possible outcomes} = 14\)

because there are 14 total pens in the bag we could potentially grab:

  • 3 red pens
  • 5 blue pens
  • 6 black pens

\(\displaystyle 3+5+6=14\)

 

Now, we can substitute into the formula.  We get

\(\displaystyle \text{probability of grabbing a blue pen} = \frac{5}{14}\)

 

Therefore, the probability of grabbing a blue pen from the bag is \(\displaystyle \frac{5}{14}\).

Example Question #81 : Data Analysis And Probability

A bag contains the following:

  • 2 blue pens
  • 3 black pens
  • 1 red pen

Find the probability of grabbing a red pen from the bag.

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle \frac{2}{3}\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle \frac{1}{6}\)

\(\displaystyle \frac{1}{5}\)

Correct answer:

\(\displaystyle \frac{1}{6}\)

Explanation:

To find the probability of an event, we will use the following formula:

\(\displaystyle \text{probability of event} = \frac{\text{number of ways event can happen}}{\text{total number of possible outcomes}}\)

 

So, given the event of grabbing a red pen from the bag, we can calculate:

\(\displaystyle \text{number of ways event can happen} = 1\)

because there is only 1 pen that we could grab from the bag.

 

We can also calculate the following:

\(\displaystyle \text{total number of possible outcomes} = 6\)

because there are 6 pens we could potentially grab (2 blue + 3 black + 1 red = 6 pens). 

 

Now, we can substitute into the formula.  We get

\(\displaystyle \text{probability of grabbing a red pen} = \frac{1}{6}\)

 

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