Question Detail
Question
In an AP, the sum of the first 20 terms is 420. If the first term is 5, find the common difference.
Correct Answer
Option A is the correct answer.
Detailed Explanation
S_n = n/2[2a + (n−1)d] → 420 = 20/2[10 + 19d] → 420 = 10[10+19d] → 42 = 10+19d → 19d=32 → d=32/19.
Hint
S_n = n/2[2a + (n−1)d].