The pages of a book starting from page 1 are summed. One of the pages has been added twice, and the total number of pages obtained is 1000. Which is the page that has been added twice?
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1. If the number are 1, 2,...50 - Sum = ((1+50)/2)*50 = 1275.. too large
2. If the number are 1, 2,...45 - Sum = ((1+45)/2)*45 = 1035.. Almost there..
So, 1035-45 = 990. This means 10 was repeated twice!
2. If the number are 1, 2,...45 - Sum = ((1+45)/2)*45 = 1035.. Almost there..
So, 1035-45 = 990. This means 10 was repeated twice!
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