Question

The sum of the first 65 odd, positive integers is?

I know the answer is 4225, but I don't know how to solve.

Answer 1

`1+3+5+7+9+11+...\\\\This\ is\ an\ atihmetic\ progression\ where\ a_1=1\ and\ d=2.\\\\The\ sum:S_n=(2a_1+(n-1)d)/(2)\cdot n\\\\S_(65)=(2\cdot1+(65-1)\cdot2)/(2)\cdot65=(2+64\cdot2)/(2)\cdot65=(2+128)/(2)\cdot65\\\\=(130)/(2)\cdot65=65\cdot65=4225`