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galibhaskar
number of numbers of the form 30a0b03 where a,b are digts which are divisible by 13 is
can you please explain this question , as a and b cannot be digits as any single digit is not divisible by 13 and if they are
For divisibility by 13 refer: http://en.wikipedia.org/wiki/Divisibility_rule#Divisibility_by_13 ∴ set of (a,b) such that 30a0b03 is divisible by 13 ={ (a,b) : 6+3a-4b=13n ; n∈N∪{0} } where a,b are digits You can do trial and error from here.