x= dad's age
y= 1/3x= boy's age
x+y=52
Substitute y=1/3x
x+1/3x=52
1 1/3x= 52
4/3x= 52
Multiply by reciprocal on both sides
(3/4)(4/3x)= (52)3/4)
x= (52*3)/4
x= 156/4
x=39 dad's age
Substitute x answer in to find boy's
y= 1/3x= 1/3(39)= (1*39)/3= 39/3= 13 boy's age
Check:
13+39= 52
Hope this helps! :)