Question

What is the value of 21 + 24 + 27 + ...... + 51?

• A. 360
• B. 380
• C. 374
• D. 396

Answer 1

Answer:

D. 396

Nth term=a + (n - 1)d N is 51 and d = 3, 51 = 21 + (n - 1) × 3 ⇒ n = 11 Sum of n terms of an AP = n/2(2a + (n - 1)d) sum=396