Posted by **Kel** on Thursday, May 15, 2008 at 7:17pm.

What is the units digit of the 100th number in this sequence: 1, 4, 8, 16, 32, 64, ...?

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**tchrwill**, Thursday, May 15, 2008 at 7:37pm
Correct me if I am wrong, but I believe you left out the actual 2nd number in this apparant series. It most likely reads 1-2-4-8-16-32-64-128-256-512-etc.

Note that after the first digit, the 1, the units digits follow the pattern of 2, 4, 8, 6 throughout.

Since the repeating series starts with the second number, we divide 99 by 4 = 24.75. The .75 indicates that the units digit of the 99th number of the repeating series, or the 100th number of the entire series, is the 3rd number of the repeating set of 2, 4, 8,6, or 8.

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**Reiny**, Thursday, May 15, 2008 at 7:45pm
I think your first number should have been 2

anyway. ... the terms end in digits 2,4,8,6,2,4,6,8

the period is 4, 100 divides evenly by 4, so it ends in the last digit of the repeat which would be 8

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