Question

Find the sum of first 10 terms of the arithmetic sequence $1,3,5,7,...........$

• A. 90
• B. 95
• C. 96
• D. 100

Answer 1

The correct option is D 100

The sum of first n terms of arithmetic series formula is given by the formula,
$S_n=\frac{n}{2}[2a+(n-1\left)d\right]$
Where n = number of terms $=10$
$a=$ first term $=1$
$d=$ common difference of A.P. $=3-1=2$
On substituting the given values in the formula, we get
$S_{10}=\frac{10}{2}[2\times 1+(10-1\left)2\right]$
$=5[2+18]$
$=5\left[20\right]$
$=100$
So, the sum of first 10 terms of the A.P. is $100$