If 15% of Y is same as 21% of Z, then 12.5% of Y is equal to what per cent of Z?

In a class, 15% of total number of students failed in Science, 25% of total number of students failed in Maths and 10% of total number of students failed in both. How much percentage of students passed in both Maths and Science?

What is 4th proportional in 9, 13 and 153?