Question

Question No. 8 How many numbers are there between 100 and 1000 such that every digit is either 5 or 7?

Answer 1

Just think in your mind that you have 3 boxes one for unit place one for tens place and one for hundred place. As we want the number between 100 and 1000 all are 3 digit no. except 1000 and we know it can be neglected.

so for unit place we have two choices either 2 or 9. same for tens place and hundred place. so the answer is 2×2×2=8.

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Answer 2

Answer:

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