allerySum of the first 20 natural numbers 1, 2, ..., 20 is
A200
B190
C220
D210
Answer & Solution
Correct answer: D. 210
1. Here a = 1, d = 1, n = 20.
2. S_20 = 20/2 * (2 + 19) = 10 * 21.
3. = 210.
4. So the sum is 210.
_Source: Selina Concise Mathematics Class 10, Ch on Arithmetic Progression (Mistral OCR'd PDF), section on sum_
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