Math Word Problems Demystified - A Self Teaching Guide

Aproportionis a statement of equality of two rations. For example,^35 ¼ 159

is a proportion. A proportion consists of four terms, and it is usually

necessary to find one of the terms of the given proportion given the other

three terms. This can be done by cross-multiplying and then dividing both

sides of the equation by the numerical coefficient of the variable.

EXAMPLE:Find the value of x:

5

6

¼

x

42

:

SOLUTION:

5

6

¼

x

42

6 x¼ 5  42 Cross-multiply

6 x¼ 210

61 x

61

¼

210

6

Divide by 6

x¼ 35

EXAMPLE:Find the value ofx:

10

x

¼

30

6

:

SOLUTION:

10

x

¼

30

6

30 x¼ 10  6 Cross-multiply

30 x¼ 60

301 x

301

¼

60

30

Divide by 30

x¼ 2

The strategy used to solve problems involving proportions is to identify

and write the ratio statement and then write the proportion.

EXAMPLE:If an airplane can travel 360 miles in 3 hours, how far can it

travel in 5 hours?

52 LESSON 6 Using Proportions