The value of 1 + 2 + 3 + .... + 10 - 50 is

For a sequence of consecutive natural numbers starting at 1, the sum of the first n terms is given by the standard identity Sn = n(n + 1) / 2, obtained by pairing the first and last terms of the sequence.

1. Here the series runs from 1 to 10, so n = 10.

2. Applying the identity: S10 = 10 × 11 / 2 = 55.

3. The expression then requires subtracting 50 from this sum: 55 − 50 = 5.

Cross-check by pairing terms directly: (1 + 10) + (2 + 9) + (3 + 8) + (4 + 7) + (5 + 6) gives five pairs that each total 11, i.e. 5 × 11 = 55 — the same sum obtained from the identity, confirming the result before the final subtraction.

So the value of 1 + 2 + 3 + … + 10 − 50 is 5.