math word problem

Question

A man is 4 times as old as his son. Five years ago, the sum of their age is 65. How old is the son?

Answer 1

Man (M) is 4 times as old as his Son (S):

M = 4*S

 

5 years ago, the sum of their age is 65.

(M-5)+(S-5) = 65

 

You now have two equations. So let's plug in M=4S (from the first equation) into our second equation:

(M-5)+(S-5) = 65

(4S-5)+(S-5) = 65

4S - 5 + S - 5 = 65

(4S+S) + (-5-5) = 65

5S - 10 = 65

 

Solve for S. 

 

Double-check by solving for M and seeing if it works.

Solve for M by plugging S back into M=4S.