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McGraw-Hill Math Grade 7 Answer Key Lesson 23.1 Calculating Probabilities
Exercises
CALCULATE
Question 1.
If there are 4 girls and 8 boys in a gym class, what is the probability of picking a girl as the person to lead the exercises?
Answer:
\(\frac{4}{12}\) = \(\frac{1}{3}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
P = \(\frac{f}{o}\)
= \(\frac{4}{4+8}\)
= \(\frac{4}{12}\)
= \(\frac{1}{3}\)
Question 2.
In a deck of 52 cards, what is the probability of drawing a king from the deck?
Answer:
\(\frac{4}{52}\) = \(\frac{1}{13}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
P = \(\frac{f}{o}\)
In a deck of 52 cards, there are 4 kings,
possible out comes 4 out of 52
= \(\frac{4}{52}\)
= \(\frac{1}{13}\)
Question 3.
There are 4 pizzas: 2 cheese, 1 vegetable and 1 everything. What is the probability that if you open a box it will be a cheese pizza?
Answer:
\(\frac{2}{4}\) = \(\frac{1}{2}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
P = \(\frac{2}{4}\)
P = \(\frac{1}{2}\)
Question 4.
George is 1 of 5 white horses that is in a group of 15 horses in total. If you see a white horse, what is the probability that it is George?
Answer:
\(\frac{1}{5}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
o = 5 white horse
f = George is one of white horse
P = \(\frac{1}{5}\)
Question 5.
You have change in your pocket: 5 quarters, 3 dimes, 2 nickels, and 4 pennies. If you pull a coin out of your pocket, what is the probability that it will be a dime?
Answer:
\(\frac{3}{14}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
5 quarters, 3 dimes, 2 nickels, and 4 pennies total 14 coins
the probability that it will be a dime
P = \(\frac{f}{o}\)
P = \(\frac{3}{5 + 3 + 2 + 4}\)
P = \(\frac{3}{14}\)
Question 6.
There are 3 different prizes at the fair: 1 first prize of $100, 3 second prizes of $50, and 5 third prizes of $10. If there are 35 participants in the contest, what is the probability that you will win a prize?
Answer:
\(\frac{9}{35}\)
Explanation:
There is a formula to figure out probability (P)
It is the number of favorable out comes (f) divided by the total number of all possible outcomes (o).
In mathematical terms P = \(\frac{f}{o}\)
f = 1 + 3 + 5 = 9 prizes
o = 35 participants
P = \(\frac{f}{o}\)
= \(\frac{9}{35}\)