ACT Math : ACT Math

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #3 : How To Find The Probability Of An Outcome

Two dice are rolled. What is the probability of getting two odd numbers on two dice?

Possible Answers:

1/4

1/2

2/3

1/6

1/8

Correct answer:

1/4

Explanation:

Two independent events that each have a probability of 1/2 of occuring.

1/2 * 1/2 = 1/4

Example Question #2 : Probability

You are at the drawing for a raffle to win a new car.  You bought 8 tickets for the raffle.  If a total of 526 tickets were sold, what is the probability that your ticket is drawn?

Possible Answers:

0.008

0.025

0.022

0.018

0.0152

Correct answer:

0.0152

Explanation:

Probability = # of Tickets You Bought / # of Tickets Sold

Probability = 8/526 = 0.0152

Example Question #3 : Probability

You roll a six sided die three times.  What are the chances that all three rolls are 2?

Possible Answers:

1/216

1/36

1/6

1/12

1/18

Correct answer:

1/216

Explanation:

Probability of each event = 1 side of die / # of sides = 1/6

Probability for multiple events = P1 * P2 * P3

1/6 x 1/6 x 1/6 = 1/216

Example Question #11 : Probability

What is the probability of NOT getting a 7 when rolling two standard six-sided dice?

Possible Answers:

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

\(\displaystyle \frac{5}{6}\)

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

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

\(\displaystyle \frac{1}{4}\)

Correct answer:

\(\displaystyle \frac{5}{6}\)

Explanation:

The sample space for rolling two six-sided dice is 36.  We can get 7 six different ways:  1,6  2,5  3,4  4,3  5,2  6,1 so the probability of getting a 7 is \(\displaystyle \frac{6}{36}\) or \(\displaystyle \frac{1}{6}\).  The probability of NOT getting a 7 is \(\displaystyle 1 - \frac{1}{6} = \frac{5}{6}\).  We can add up all the things we want or we can subtract from 1 what we don't want. 

Example Question #121 : Data Analysis

Jack has a bag with 16 marbles in it. 8 white marbles, 6 green marbles, and 2 red marbles. Jack reaches into the bag and randomly chooses two marbles replacing each marble back in the bag after. What is the probability that he chooses 1 white marble with and 1 red marble?

Possible Answers:

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

\frac{1}{16}\(\displaystyle \frac{1}{16}\)

\frac{1}{8}\(\displaystyle \frac{1}{8}\)

\frac{3}{5}\(\displaystyle \frac{3}{5}\)

\frac{1}{4}\(\displaystyle \frac{1}{4}\)

Correct answer:

\frac{1}{16}\(\displaystyle \frac{1}{16}\)

Explanation:

The probability of choosing 1 white marble is \frac{1}{2}\(\displaystyle \frac{1}{2}\).

The probability of choosing a red marble is \frac{1}{8}\(\displaystyle \frac{1}{8}\).

To find the chances of both events happneing you must multiply the probabilities together. 

Example Question #12 : Probability

If a marble is randomly chosen from a bag that contains exactly 12 purple marbles, 3 red marbles, and 10 blue marbles, what is the probability that the marble will NOT be blue?

Possible Answers:

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

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

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

\frac{5}{13}\(\displaystyle \frac{5}{13}\)

\frac{3}{5}\(\displaystyle \frac{3}{5}\)

Correct answer:

\frac{3}{5}\(\displaystyle \frac{3}{5}\)

Explanation:

To find the probability of a marble being chosen, we divide the number of the certain marble by the total number of marbles. In this case, we are finding the probability of NOT choosing a blue marble, or the probability of choosing a purple or red marble. The probability of choosing a purple marble is \frac{12}{25}\(\displaystyle \frac{12}{25}\), and that for a red marble is \frac{3}{25}\(\displaystyle \frac{3}{25}\). Together, this adds up to \frac{15}{25}\(\displaystyle \frac{15}{25}\), which is reduced down to \frac{3}{5}\(\displaystyle \frac{3}{5}\).

Example Question #12 : Probability

Suppose 30 percent of pet owners surveyed have both a cat and a dog, and 10 percent have neither. If there were twice as many pet owners who own only a dog as there were owners who only had a cat, what is the probability that a pet owner selected at random owns only a dog?

Possible Answers:

\(\displaystyle 0.2\)

\(\displaystyle 0.1\)

\(\displaystyle 0.6\)

\(\displaystyle 0.4\)

\(\displaystyle 0.5\)

Correct answer:

\(\displaystyle 0.4\)

Explanation:

If 30% of owners have both a cat and a dog and 10% have neither, that leaves 60% of owners who either have only a cat or only a dog. \(\displaystyle 1 - 0.3 - 0.1 = 0.6\)

There are twice as many owners that only own a dog as owners that only own a cat. Thus, \(\displaystyle 2c = d\).

The total number of cat-only and dog-only owners make up 60% of those surveyed. Thus, \(\displaystyle c + d = 0.6\)

Substitute \(\displaystyle 2c\) for \(\displaystyle d\) in the second equation. \(\displaystyle c + 2c = 0.6\)

Solve for \(\displaystyle c\)\(\displaystyle c= 0.2\)

Plug answer into first equation to get value of \(\displaystyle d\), the probability of selecting an owner that only has a dog.

Example Question #122 : Data Analysis

What is the probability of not getting an even number less than six when rolling two six-sided dice?

Possible Answers:

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

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

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

\(\displaystyle \frac{5}{6}\)

\(\displaystyle \frac{8}{9}\)

Correct answer:

\(\displaystyle \frac{8}{9}\)

Explanation:

The sample space for rolling two six-sided dice is \(\displaystyle 36\).

Even numbers less than 6 are 4 and 2:

\(\displaystyle 2: 1,1\)

\(\displaystyle 4: 1,3 \; \; \; 2,2 \; \; \; 3,1\)

So the probability of getting an even number less than six is \(\displaystyle \frac{4}{36} = \frac{1}{9}\)

So the probabilty of not getting an even number less than six is

 \(\displaystyle 1 - \frac{1}{9}\) or \(\displaystyle \frac{8}{9}\)

Example Question #12 : Probability

There are 20 people going to a company party. One person is chosen at random to bring the cake. However, no one can bring a cake two parties in a row. Assuming the same 20 people go to every company party, what is the probability that Leslie, who did not bring the cake last time, will be chosen?

Possible Answers:

\(\displaystyle \frac{1}{21}\)

\(\displaystyle \frac{1}{20}\)

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

\(\displaystyle 0\)

\(\displaystyle \frac{1}{19}\)

Correct answer:

\(\displaystyle \frac{1}{19}\)

Explanation:

This is a probability question. All you have to account for is that one of the twenty people at this party brought a cake last time so they will not need to bring it this time. Therefore we take one person away from the twenty leaving nineteen people. Leslie has a \(\displaystyle \frac{1}{19}\) probabiity of being chosen.

Example Question #13 : Probability

Given a standard deck of 52 playing cards, where half (clubs and spades) are black and half (hearts and diamonds) are red, what is the probability of picking three black cards in a row if the cards are not replaced?

Possible Answers:

\(\displaystyle \frac{2}{17}\)

\(\displaystyle \frac{6}{23}\)

\(\displaystyle \frac{5}{19}\)

\(\displaystyle \frac{3}{52}\)

\(\displaystyle \frac{11}{45}\)

Correct answer:

\(\displaystyle \frac{2}{17}\)

Explanation:

\(\displaystyle 26\; black \; cards + 26 \; red \; cards = 52 \; total \; cards\)

Probability that first card is black:  \(\displaystyle \frac{26}{52} = \frac{1}{2}\)

Now there are 25 black cards remaining in the deck.

Probability that second card is black: \(\displaystyle \frac{25}{51}\)

Now there are 24 black cards remaining in the deck.

Probability that third card is black:  \(\displaystyle \frac{24}{50} = \frac{12}{25}\)

The probability of getting three black cards in a row is

\(\displaystyle \frac{1}{2} * \frac{25}{51} * \frac{12}{25} = \frac{300}{2550}=\frac{2}{17}\)

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