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Can you find a quick and elegant way to add the numbers from 1 to 28 ?
In other words, what is the sum you obtain in the following case:
1 + 2 + 3 + ....... + 28 =
Answer: 406
Solution:
Here's an elegant way:
1 + 28 = 29
2 + 27 = 29
3 + 26 = 29
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14 + 15 = 29
Adding the above equations gives
1 + 2 + 3 + ....... + 28 = 14 × 29 = 406
Food for thought:
The general formula is:
1 + 2 + 3 + ....... + n = n (n + 1) / 2.
Is the formula valid when n is an odd integer?
Try the Quiz : Puzzles & Brain Teasers : Add Quickly
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