Question

Calculate:-1-2+3-4+5-6+...+199-1000
please give full Answer​

Answer 1

Step-by-step explanation:

$additon \: of \: consecutive \: numbers = \frac{n(n + 1)}{2}$

$n = 199 \\ \frac{199 \times (199 + 1)}{2} \\ \frac{199 \times 200}{2} = \frac{39800}{2} \\ = 19900 \\ now \: we \: subtract \: this \: number \: and \: 1000 \\ = 19900 - 1000 \\= 18900$

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