[Math] sum of all positive odd integers less than $1000$

Question

If the sum of all positive even integers less than $1000$ is $ A $ , what is the sum of all positive odd integers less than $1000$?

Answer 1

\begin{align} \underbrace{1}_{0+1}+\underbrace{3}_{2+1}+5+\cdots+\underbrace{999}_{998+1}&=\underbrace{(0+1)+(2+1)+\cdots+(998+1)}_{\text{500 terms}}=\\ &=\underbrace{0+2+4+\cdots+998}_{A}+\underbrace{1+1+\cdots+1}_{500 \text{ ones}}=A+500 \end{align}