Question

(a) Find the sum of the first 20 odd numbers
b) Find the sum of odd numbers from 21 to 50​

Answer 1

sum of first 20 numbers:

$s=\frac{n}{2}[2a_1+(n-1)d] s=10[2+(19)2]s=10[2+38]s=10[40]s=40$

sum of odd no from 21 to 50:

$s=\frac{n}{2}(a+l)\\s=\frac{15}{2}(20+50)\\s=525$

Answer 2

Answer:

1 .Answer: The sum of first 20 odd natural numbers is 400.

Step-by-step explanation:

2. answer. explanation. If the number is starting from 1 then you can do simply n^2. for example: if n=6 like 1,3,5,7,9,11 then it's sum will be 6^2=36. But if odd number series not start from 1 then formula will be sn=n/2(2a+(n-1)d).