Numerical Ability - Simplification & Approximation
Find the sum of the first 20 natural numbers.
Find the sum of the first 20 natural numbers.
medium Q14 of 15
Step-by-Step Solution
Step 1: Recall the formula
Sum of first n natural numbers = n(n+1)/2.Step 2: Compute for n = 20
(20 × 21) ÷ 2 = 420 ÷ 2 = 210.Final Answer:
210 → Option D.Quick Check:
Pairing method: (1+20)=21, (2+19)=21, … 10 pairs × 21 = 210 ✅
Quick Trick: n(n+1)/2 gives the exact sum; pairing terms gives a quick check.
Common Mistakes:
- Forgetting to divide by 2 or miscounting pairs.
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