Arithmetic Reasoning - Expert Level Question 31 – answer, explanation & discussion

First ten odd numbers form an arithmetic progression of the form 1,3,5,7,9......

here a = first term = 1

d = common difference = 2

Average of first n numbers = (2a + (n - 1)d)/2

n th term of the AP = a + (n - 1)d

Substituting a = 1, d = 2 and n = 10 in the above formulas

average of first 10 numbers = 10

10 th term of the AP = 19

Therefore average of first 10 terms is 19 - 10 = 9 greater than the last term. Hence the average is greater than the sum by

9/19 X 100 = 900/19 %