Cross Multiplication

Front

What is cross multiplication?

Back

Cross multiplication is a method used to solve proportions by multiplying the numerator of one fraction by the denominator of the other fraction.

Tags

CCSS.7.RP.A.3

Front

How do you set up a proportion?

Back

A proportion is set up by stating that two ratios are equal, for example, a/b = c/d.

Tags

CCSS.7.RP.A.2A

Front

If 2 out of 10 students enjoy basketball, how do you find how many enjoy it in a class of 25?

Back

Set up the proportion: 2/10 = x/25, then cross multiply to find x.

Tags

CCSS.7.RP.A.2B

Front

What is the first step in solving a proportion using cross multiplication?

Back

The first step is to set the two ratios equal to each other.

Tags

CCSS.7.RP.A.3

Front

In the proportion 12/100 = x/N, what does N represent?

Back

N represents the total number of scholars surveyed.

Tags

CCSS.7.RP.A.2C

Front

How do you find the total number of students surveyed if 12 out of 100 like pizza and 54 like pizza?

Back

Set up the proportion: 12/100 = 54/N, then cross multiply to solve for N.

Tags

CCSS.7.RP.A.3

Front

What is the solution to the proportion 3/4 = x/8?

Back

x = 6, found by cross multiplying.

Tags

CCSS.7.RP.A.2C

Front

If a recipe requires 2 ½ cups of flour for 2 dozen cookies, how do you find the amount for 15 dozen?

Back

Set up the proportion: 2.5/2 = x/15, then cross multiply to find x.

Tags

CCSS.7.RP.A.3

Front

What is the result of cross multiplying 4/5 = x/10?

Back

x = 8, since 4*10 = 5*x.

Tags

CCSS.4.NF.A.1

CCSS.3.NF.A.3B

Front

How do you check if your answer to a proportion is correct?

Back

You can check by substituting your answer back into the original proportion to see if both sides are equal.

Tags

CCSS.7.RP.A.2A