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Summing Ones (Posted on 2013-02-27)

Find the sum
1+11+111+.......+111..111(n digits)

No Solution Yet Submitted by Danish Ahmed Khan

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re: No Subject (spoiler)

| Comment 3 of 4 |

(In reply to No Subject by Ady TZIDON)

sn=1/81*(10^(1+n)-9n-1)

then, when n=3, for example,

sn = (10^4 - 27 - 1) / 81 = 123.111111111111...

The formula could be changed to either:

sn=[1/81*(10^(1+n)-9n-1)]

where the square brackets indicate the floor function, or

sn=1/81*(10^(1+n)-9n-1) - 1/9

as the excess over an integer is always 1/9.

Posted by Charlie on 2013-02-27 13:27:15

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