
The sum of first 20 odd natural numbers is
A. 100 B. 210 C. 400 D. 420 Answer: Option CShow Answer
Solution(By Apex Team)
First 20 odd natural numbers are 1, 3, 5, 7, 9, 11, 13, 15, . . . . ., 39
Here a = 1, d = 2, n = 20
$\begin{aligned}&\therefore S_{20}=\frac{n}{2}[2a+(n-1)d]\\
&=\frac{20}{2}[2\times1+(20-1)\times2]\\
&=10(2+38)\\
&=10\times40\\&=400\end{aligned}$
Related Questions On Progressions
How many terms are there in 20, 25, 30 . . . . . . 140?
A. 22B. 25
C. 23
D. 24
Find the first term of an AP whose 8th and 12th terms are respectively 39 and 59.
A. 5B. 6
C. 4
D. 3
Find the 15th term of the sequence 20, 15, 10 . . .
A. -45B. -55
C. -50
D. 0
The sum of the first 16 terms of an AP whose first term and third term are 5 and 15 respectively is
A. 600B. 765
C. 640
D. 680