The age of Oscar is 1/3of his sister. after 12 years his age will be half that of his sister. What is Oscar's current age

Let's denote:

Age of Oscar : x

Age of Oscar's sister : y

Then, we have:

3x = y (1)

2 (x + 12) = y + 12 (2)

Substitute y from (1) into (2), then:

=> 2 (x + 12) = 3x + 12

=> 2x + 24 = 3x + 12

=> x = 24 - 12

=> x = 12

=> Oscar's current age: 12