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49. Find the sum of first 2019 odd numbers. |
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Answer» The answer is: 2,039,190. For any addition of consecutive numbers from 1 there’s a simple way of working this out. It’s easier if the final number is even, so take the case of 1 to 6. 1+2+3+4+5+6 = 1+6 + 2+5 + 3+4 All these pairs add to the same (the sum of the first and last) and there are half as many as the total. In other words: Sum of 1 to N(even) = (1+N) * (N/2) For final odd numbers there is one less pair which is replaced by the central value, so Sum of 1 to N(odd) = (1+N) * ((N-1)/2) + ((N+1)/2) |
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