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

Let Zia's current age be Z. Ali's age is Z-10. Five years ago, their ages were (Z-15) and (Z-5). The ratio (Z-15)/(Z-5) = 1/2, which solves to Z=25. Options A and B are incorrect calculations.