The average of five consecutive odd numbers is m. If the next three odd numbers are also included, then what is the increase in the average?

Let the first odd number is x. Then the five consecutive odd numbers will be

x, x+2, x+4, x+6, x+8 whose sum is

5x + 20 and the average will be (5x + 20 )/5 = x+ 4 which is given to be M. So x= M-4

the next 3 odd numbers would be

x+10, x+12, x+14 whose sum is 3x+36

The sum of 10 numbers is (5x + 20)+(3x+36)

= 8x + 56. So the new average is 8(x+7)/8 = x+7

on substituting x = M-4 in new average, we get

M-4+7 = M+3

The new average is M+3
Increment in the average = m + 3 - m = 3