DRDO Multi tasking staff Model paper 4

First term of AP (a) = 1
Common difference (d) = 1
Number of terms (n) = 50
∴ Sum of first n terms of an AP (Sn) is given by:
Sn=

n

2

{2a + (n-1) d}
⇒S50 = (50/2) × [(2 × 1) + {(50 – 1) × 1}]
⇒S50 = 25 × {2 + 49} = 1275
Thus, sum of first 50 terms of the given AP is 1275.