What is the sum of first 20 multiples of 2?

The sum of first n terms of arithmetic series formula can be written as,

$S_n=\frac{n}{2}[2a+(n-1)d]$

Where n = number of terms $\Rightarrow$ 20

a = first odd number $\Rightarrow$ 2

d = common difference of A.P. $\Rightarrow$ 2

Apply the given data in the formula,

$S_{20}=\frac{20}{2}[2\times 2+(20-1)2]$

$=10[4+(19)2]$

$=10[4+38]$

$=10[42]$

$=420$

So, the sum of first 20 multiples of 2 is 420.