Write the sum of 20 terms of the series: `1+1/2(1+2)+1/3(1+2+3)+ `

Explanation

We have given the series as `1+1/2(1+2)+1/3(1+2+3)+.....`upto 20 terms

Then it can also be written as `1+(3/2)+(6/3)+(10/4)+.....`upto 20 terms

Now , this is an A.P. series .

Hence formula for sum of n^th term is

`S_n=(n/2)[2a+(n-1)d]`

Now here, `a=1, d=1/2` and `n=20`

So,

`S_20=(20/2)[2+(20-1)/2]`

...