What is the sum of the first 20 odd numbers 1, 3, 5, ... ?
Answer and explanation
Correct answer: B. 400
- Step 1: The sum of the first n odd numbers equals n squared.
- Step 2: With n = 20 the sum is 400 (check: 20 terms, mean 20, 20 x 20 = 400).
Answer
400.
Why not the others: n(n + 1) gives the sum of the first n whole numbers, and the other values miscount the pairs.
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