GATE | GATE-CS-2014-(Set-2) | Question 65

What is the average of all multiples of 10 from 2 to 198?
(A) 90
(B) 100
(C) 110
(D) 120


Answer: (B)

Explanation:

From 2 to 198 there are 19 multiples of 10.

These are 10,20,30.....180,190.

This is an A.P series, whose sum is (n/2{a1 + aN}), 
where a1 and aN are the 1st and last terms respectively.

Putting in the formula,

a1 = 10, aN = 190.

Sum = Sn = (19/2{10 + 190 }) = 1900

Average = Sum / Total number = 1900 / 19 = 100. 


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