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

A360

B380

C374

D396

Answer:

D. 396

Read Explanation:

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


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