1+2+3+4+5….+14+15 is equal to which number?

A. 75
B. 93
C. 100
D. 120

Sum of the series formula

The sum of 1+2+3+4+5….+15 is equal to 120

As we have the formula Sn = n/2 [a+l]

If Sn is the sum of n terms of an A.P. whose first term is “a” and the last term is “l” ,

then
Sn = n/2 [a+l]

Putting the above values

Sum of the n terms= 15/2 [1+15]

=> Sum of the n terms= 15/2 [16]

=> Sum of the n terms= 15 x [8] = 120

So, the sum of 1+2+3+4+5….+15 is 120 which is the right option