What is the average of first 100 multiples of 5 ?

Question

Out of three given numbers , the first one is twice the second and three times the third.
If the average of these numbers is 88, then what is the difference between first and third ?

Answer 1

5x1 + 5x2 + 5x3 + 5x4 ..... 5x100 = 5 * (1 + 2 + 3 + 5 .... + 100)
= 5 * (sum of n numbers)

For calculating the sum of n numbers we have the formula
i.e (n * (n + 1)) / 2

apply the formula in the above equation.
where n = 100
so
= 5 * (100 * (100 + 1)) / 2
= 5 * (50 * 101)
= 5 * 50 * 101
= 25250
This the sum of the first 100 positive number which is multiples of 5.

And for average:
= 25250 /100
= 252.50

Answer 2

Answer: 252.5

Solution: ((5 x 1) + (5 x 100)) / 2 = 252.5

Answer 3

(5*((100*101)/2))/100=252.5