Jacob is one fourth the age of his dad. In three and a half years he will be one third the age of his dad. How old is Jacob now?

Question

I solved this problem and got that his dad was 7 years old. I know I messed up with the variables and that Jacob is 7, but I just can't figure out where since my equations were set up properly (or at least I believe so). I plugged in 1/4D for J in the third equation and came out with the answer: D=7.

J=1/4D

D=4J

J+3.5=1/3(D+3.5)

Answer 1

j = d/4

d = 4j

j+ 3.5 = (d+3.5)/3

3j = 10.5 = d +3.5

3j = 10.5 = 4j +3.5

4j - 3j = 10.5 -3.5 = 7

j = 7

d = 28

in 3 1/2 year

j = 10.5 and d = 31.5

10.5 = 1/3 of 31.5

31.5/3 = 10.5

You got it almost right. dad's 28, son is 7

in 3 1/2 years, dad will be 31 1/2 and son will be 10 1/2

3 x 10 1/2 = 31 1/2