Hisoblang: 1 - 2 + 3 - 4 + 5 - ... + 99 - 100

We can group the terms in pairs:

\[ (1 - 2) + (3 - 4) + (5 - 6) + \dots + (99 - 100) \]

Each pair sums to -1:

\[ (-1) + (-1) + (-1) + \dots + (-1) \]

To find the number of pairs, we have numbers from 1 to 100, which is 100 numbers. Since we are pairing them up, there are \( \frac{100}{2} = 50 \) pairs.

So, the sum is the sum of 50 negative ones:

\[ 50 \times (-1) = -50 \]

Ответ: -50