Numbers - Arithmetic Aptitude Questions and Answers

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The sum all even natural numbers between 1 and 31 is:

128

240

512

Answer : Option C

Explanation :

Required sum = (2 + 4 + 6 + ... + 30)

This is an A.P. in which a = 2, d = (4 - 2) = 2 and l = 30.

Let the number of terms be n. Then,

t_n = 30 a + (n - 1)d = 30

2 + (n - 1) x 2 = 30

n - 1 = 14

n = 15

S_n = $\frac { n } { 2 }(a+1)$ = $\frac { 15 } { 2 }* (2+30)$ =240

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