Question

what is the sum of first 1000 positive integers​

Answer 1

$required \: sum = \frac{n}{2}(a + l) \: where \: n \: is \\ the \: total \: number \: of \: numbers \: in \: total \\ \\ (a) \: is \: the \: 1st \: term \: and \: (l) \: is \\ the \: last \: term \\ \\ \\ \\ \\ = \frac{1000}{2}(1 + 1000) \\ = 500 \times 1001 \\ 500500$