Let Jonah's age be 10a + b
Reversing the digits gives 10 b + a
So we have this
(10b + a) / 3 + 20 = 10a + b
(10b + a) / 3 = 10a + b - 20 multiply both sides by 3
10b + a = 30a + 3b - 60 simplify as
60 = 29a - 7b
Note that this will be true when a = 4 and b = 8
So....his current age = 10 (4) + 8 = 48
Note that when he reverses the digits and divides by 3 he gets 28 adding 20 gives 48 !!!