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The number of ordered pairs (m,n) m,n€{1,2,3,...,100} such that 7 m +7 n is divisible by 5 is ___

The number of ordered pairs (m,n) m,n€{1,2,3,...,100} such that 7+7n is divisible by 5 is ___

Grade:12

1 Answers

Deepak Kumar Shringi
askIITians Faculty 4404 Points
6 years ago
to divisible by 5 unit digit must be either zero or 5 here exponent of 7 can be
(7,9,3,1) at unit digit and to make sum 0 or 5 it should be
(7+3) or (9+1)
to take 7+3
(71+73) and (75+73)...................................(799+73)

(71+77)...........................................................(799+77)
in this way you can apporach it



























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