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JEE Main Mathematics question

MathematicsPermutations and CombinationsJEE Main

Number of -digit numbers (the repetition of digits is allowed) which are made using the digits and , and are divisible by , is equal to

Answer: 21

Solution

Divisible by means divisible by (last digit ) and by (digit sum divisible by ). The digits leave remainders modulo ; the last digit has remainder , so the first three digits need a sum

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Question ID VK-020910