PRC-2 · Chapter 3 · Question 20 of 45
The first and last terms of an arithmetic progression are 20 and 100, respectively. If the total sum of all terms is 300, what is the exact common difference?
Test yourself: pick an answer
Reveal answer & explanation
Correct answer: B) 20
Explanation
First, find n using S = (n/2)(a + l): 300 = (n/2)(20 + 100) -> 300 = 60n -> n = 5. Then, use the last term formula l = a + (n-1)d: 100 = 20 + 4d -> 80 = 4d -> d = 20.
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