Math Word Problems Demystified - A Self Teaching Guide

2 x¼ 18

21 x

21

¼

18

2

x¼ 9

Find the other number.

y¼xþ 8

y¼ 9 þ 8

y¼ 17

Hence, the numbers are 9 and 17.

EVALUATION: Check the second equation.

xþy¼ 26

9 þ 17 ¼ 26

26 ¼ 26

EXAMPLE:The sum of the digits of a two-digit number is 15. If the digits
are reversed, the new number is 9 more than the original number. Find the
number.

SOLUTION:

GOAL: You are being asked to find a two-digit number.

STRATEGY: Letx¼the ten’s digit

y¼the one’s digit

10 xþy¼original number

10 yþx¼new number with digits reversed

Since the sum of the digits of the number is 15, the first equation is

xþy¼ 15

LESSON 18 Using Two Equations 209