Math Word Problems Demystified - A Self Teaching Guide

3. Letx¼Mike’s age andxþ 4 ¼Mark’s age.

xþxþ 4 ¼ 20

2 xþ 4 ¼ 20

2 xþ 4 
 4 ¼ 20 
 4

2 x¼ 16

21 x

21

¼

16

2

x¼ 8 ðMike’s age)

xþ 4 ¼ 8 þ 4 ¼ 12 ðMark’s age)

4. Letx¼Mary’s age andxþ 12 ¼Marie’s age; thenx
   9 ¼Mary’s
   age andxþ 12
   9 ¼Marie’s age 9 years ago.

2 ðx
 9 Þ¼xþ 12 
 9

2 x
 18 ¼xþ 3

2 x
x
 18 ¼x
xþ 3

x
 18 ¼ 3

x
 18 þ 18 ¼ 3 þ 18

x¼ 21 ðMary’s age)

xþ 12 ¼ 21 þ 12 ¼ 33 ðMarie’s age)

5. Letx¼number of years ago when Bill was three times as old as Sam;
   then 18
   x¼Sam’s age and 24
   x¼Bill’s agexyears ago.

3 ð 18 
xÞ¼ 24 
x

54 
 3 x¼ 24 
x

54 
 3 xþx¼ 24 
xþx

LESSON 12 Solving Age Problems 127