How old until Bala's father is three times older

[Johnx1]

Bala is 11 years old. His father is 37 years old. In how many years' time will Bala's father be three times as Bala.

My answer:

Bala = B
Father = F

so,

B = 11
F = B + 26
F = 3B

=>3B = B + 26
= B = 13

So, the answer is when bala is 13 and the father is 39.However, when I did it in a different way, where I did F = 48 - B, I get a difference answer.

Is the first way how I did it mathematically correct?

 

[Greg]

Bala is 11 years old. His father is 37 years old. In how many years' time will Bala's father be three times as Bala.

My answer:

Bala = B
Father = F
so,
B = 11
F = B + 26
F = 3B
=>3B = B + 26
= B = 13
So, the answer is when bala is 13 and the father is 39.

However, when I did it in a different way, where I did F = 48 - B, I get a difference answer.
Is the first way how I did it mathematically correct?

Yes, because the difference between the two ages is 26 no matter the value of B. So all you really need is

F = B + 26
F = 3B

=>3B = B + 26
= B = 13

Since 13 - 11 = 2 the answer to the original problem is "In 2 years time Bala's father will be three times as old as Bala."

Another method would be solving 3(11 + x) = 37 + x for x.