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1.What should be added to $15^{81}$ to make it divisible by 7 ? Suggest a general technique to counter problems like this.

2.For how many two-digit numbers, the sum of the digits is greater than the product of the digits?

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    How about 7 - 15^{81}?2010-10-29
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    Hmm not getting what you meant ??2010-10-29
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    I mean that 15^{81} + (7 - 15^{81}) is divisible by 7.2010-10-29
  • 0
    Wow, that's intuitive but unfortunately that's not the solution set :)2010-10-29
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    If any of the answers you get help you, you could accept them by clicking the ghostly check mark beside them.2010-12-22

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