Question

john is now three times as old as his brother Sam. In five years, john will be twice as old as Sam will be then. Find their present ages.

Answer 1

j=john's age now
s=sam's age now

j=3 times s
j=3s
in five years (j+5,s+5)
j+5=2 times (5+s)
j+5=2(s+5)
j+5=2s+10
subtract 5 from both sides
j=2s+5
use other equation
j=3s
j=2s+5
subsitute
3s=2s+5
subtract 2s
s=5

sam=5
j=3s
j=3 times 5
j=15


john=15
sam=5