Question

Find the sum of first 30 positive multiples of 3 ?

Answer 1

`1395`

Explanation:

Your question is:

`3+6+9+...+90`

We can write the sum as

`sum_(n=0)^(29)3n+3`

Plugging this into a calculator, we get

`sum_(n=0)^(29)3n+3=1395`

So, `3+6+9+...+90=1395`