What is the sum of all whole numbers from 1 to 80?
Answer and explanation
Correct answer: B.
- Step 1: Pair the first and last numbers: each pair sums to 81. Step 2. There are 40 pairs, so the sum is 80 × 81 ÷ 2 = 3240. **Answer: . Why not the others:** is what you get if you use n²/2. is what you get if you forget to halve. is what you get if you stop at 79.
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