861 CandlesMath brain teasers require computations to solve.
I have always had the correct number of candles on each of my birthday cakes. I have had exactly one birthday cake for each year of my life. If I have blown out a total of 861 candles thus far, how old am I?
Can you find the answer without just adding up numbers until you reach 861?
Hint1+ 2+ 3 + ... + n = 861 .
To sum up the first n positive integers, the following formula is helpful:
Sum = n*(n+1)/2
Think of it this way: find the smaller of two consecutive positive integers such that half the product of the integers is 861.
If n = 41 , we see that:
S = 41(41+1)/2 = 41(42)/2 = 861.
Thus, if you add up the integers from 1 to 41, you will get a total of 861.
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