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# the tens' digit of 9^20 is 0m what is the tens' digit of

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the tens' digit of 9^20 is 0m what is the tens' digit of [#permalink]  21 Jul 2006, 12:32
the tens' digit of 9^20 is 0m what is the tens' digit of 9^19?
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Kudos [?]: 37 [0], given: 0

9^1 = 9
9^2 = 81
9^3 = 729

so last digit will be 9 when power is odd and will be 1 when power is even.

So last two digits of 9^20 = 01
Last two digits of 9^19 = X9

Multiplying X9 to 9 should lead to last a number with last two digits as X9.
This is possible only if X is 8.
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SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

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