How many numbers between 99 and 1000(both excluding) can be formed such that (a) every digit is either 3 or 7 (b) there is no restriction (c) no digit is repeated (d) the digit in hundred’s place is 7 (e) the digit 7 does not appear at any place (f) at least one of the digit is 7
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Step-by-step explanation:
The middle digit can be any one of the 10 digits from 0 to 9. The digit in hundred's place can be any one of the 9 digits from 1 to 9. Therefore, by the fundamental principle of counting, there are 10 × 9 = 90 numbers between 99 and 1000 having 7 in the unit's place.
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