Example of Word problem:
There is a man who is 21 years older than his son. 5 years ago he was four times as old as his son. How older are both now?
Solution:
Step 1. Let x = Son's Age Now
Step 2. Then,
x + 21 = Father's Age Now
x - 5 = Son's Age Five Years Ago
(x + 21) - 5 = Father's Age Five Years Ago
Step 3. 5 years ago the father was four times as old as his son. (x + 21) - 5 = 4(x - 5)
Step 4. (x + 21) - 5 = 4(x - 5)
x + 16 = 4x - 20
x - 4x = -20 - 16
-3x = -36
x = 12 years
Solving for the other unknowns:
x + 21 = 12 + 21
x + 21 = 33 years
Answers: Son's Age Now = 12 years
Father's Age Now = 33 years
Step 5. The man is 21 years older than his son.
12 + 21 = 33 years
Five years ago he was four times as old as his son.
33 - 5 = 28 = 4(12 - 5) = 4 x 7
Thus, the answers check.