InterviewSolution
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InterviewSolution
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If the number of ways of selecting n cards out of unlimited number of cards bearing the number 0,9,3, so that they cannot be used to write the number 903 is 96, then n is equal toA. 3B. 4C. 5D. 6 |
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Answer» Correct Answer - C We cannnot write 903. If in the selection of n cards, we get either (9 or 3), (9 or 0), (0 or 3), (only 0), (only 3) or (only 9). For (9 or 3) can be selected `=2xx2xx2xx . . .xxn` factors `=2^(n)` Similarly, (9 or 0) or (0 or 3) can be selected `=2^(n)` In the above selection (only 0) or (only 3) or (only 9) is repeated twice. `therefore`Total ways `=2^(n)+2^(n)+2^(n)-3=93` `implies3*2^(n)=96implies2^(n)=32=2^(5)` `thereforen=5`. |
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