alleryThe sum of the first 20 terms of an A.P. with first term 2 and common difference 3 is:
A305
B590
C620
D610
Answer & Solution
Correct answer: D. 610
We have Sₙ = n/2[2a+(n−1)d].
That is Sₙ = 20/2[4 + 19·3].
That is Sₙ = 10[4+57].
So Sₙ = 610.
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