The sum of first 20 odd natural numbers is
A. 100
B. 210
C. 400
D. 420
Answer: Option C
Solution(By Examveda Team)
First 20 odd natural numbers are 1, 3, 5, 7, 9, 11, 13, 15, . . . . ., 39Here a = 1, d = 2, n = 20
$$\eqalign{ & \therefore {S_{20}} = \frac{n}{2}\left[ {2a + \left( {n - 1} \right)d} \right] \cr & = \frac{{20}}{2}\left[ {2 \times 1 + \left( {20 - 1} \right) \times 2} \right] \cr & = 10\left( {2 + 38} \right) \cr & = 10 \times 40 \cr & = 400 \cr} $$
Related Questions on Progressions
Find the first term of an AP whose 8th and 12th terms are respectively 39 and 59.
A. 5
B. 6
C. 4
D. 3
E. 7
The sum of the first 16 terms of an AP whose first term and third term are 5 and 15 respectively is
A. 600
B. 765
C. 640
D. 680
E. 690
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