Is there a shortcut method to working out the sum of n consecutive positive integers?
Firstly, starting at $1 ... 1 + 2 + 3 + 4 + 5 = 15.$
Secondly, starting at any other positive integer ...($10$ e.g.): $10 + 11 + 12 + 13 = 46$.
Answer
Take the average of the first number and the last number, and multiply by the number of numbers.
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