Question

The sum of first 20 odd numbers is

• A. 20
• B. 100
• C. 400
• D. 313

Answer 1

The correct option is C 400

The first number odd =$1,3,5,7,9-37,39$
Here,the first term is $1$ and
Common dofference is $2$
The series is in AP
$\therefore S_n=\frac{n}{2}\times [a+(n-1)\times 1]$
$\therefore S_{20}=\frac{20}{2}\times [1+(20-1)\times 2]$
$\therefore S_{20}=400$