Ali is younger than Zia by 10 years. If 5 years back their ages were in the ratio 1:2, how old is Zia?  

   (A) 20 years  

   (B) 15 years  

   (C) 25 years  

   (D) None of these 

Explanation

Let’s break this down step by step:

1. Let Ali’s current age be A and Zia’s current age be Z.
2. Since Ali is younger than Zia by 10 years, we can write an equation: A = Z – 10
3. We know that 5 years back, their ages were in the ratio 1:2. So, we can set up another equation based on their ages 5 years back: (A-5)/(Z-5) = 1/2
4. Cross-multiply and simplify the equation: 2A – 10 = Z – 5
5. Substitute the expression for A from step 2 into the equation in step 4: 2(Z-10) – 10 = Z – 5
6. Simplify and solve for Z: 2Z – 20 – 10 = Z – 5 –> Z = 25

So, Zia is currently 25 years old.