Two numbers X and Y are respectively 20% and 28% less then a third number Z. By what percentage is the number Y less than that of the number X?

Here, Z = 100, X = 80 and Y = 72
Now according to the formula,
Percentage change = (New amount - Original amount)/Original amount
= [(80 - 72)/80] x 100%
= (8/80) x 100%
= 10%
∴ Y is less by X = 10%