Medium
Find the sum of the first 14 terms of the AP with first term 4 and common difference 5.
Explanation
Explanation
The sum of the first n terms of an AP is Sₙ = n/2 × [2a + (n-1)d]. Here n = 14, a = 4, d = 5. So S = 14/2 × [2(4) + (14-1)(5)] = 14/2 × [8 + 65] = 14/2 × 73 = 511.
PRO TIP
Re-check your working by substituting the answer back into the original question.