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Permutations and Combinations question

2021 · 22 Jul · Shift 2 · Q39
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Permutations and Combinations question

2021 · 22 Jul · Shift 2 · Q39

JEE MainMathematicsPermutations and CombinationsNumerical+4 / −1
If the digits are not allowed to repeat in any number formed by using the digits 0, 2, 4, 6, 8, then the number of all numbers greater than 10,000 is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
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Correct answer: 96

  1. We are given the digits {0,2,4,6,8}\{0,2,4,6,8\}{0,2,4,6,8} and no digit may repeat.

  2. We need the number of all numbers greater than 10,00010{,}00010,000.

  3. Since the available digits are only 5 digits total, any number greater than 10,00010{,}00010,000 formed from these digits without repetition must be a 5-digit number.

  4. So we count all 5-digit numbers that can be formed using all five digits 0,2,4,6,80,2,4,6,80,2,4,6,8 exactly once, with the condition that the first digit cannot be 000.

  5. Total permutations of the 5 digits: 5!=1205! = 1205!=120

  6. Count the invalid arrangements where 000 is in the first place. Fix 000 in the first position, then arrange the remaining 4 digits: 4!=244! = 244!=24

  7. Therefore, valid 5-digit numbers are 120−24=96120 - 24 = 96120−24=96

  8. Hence, the number of all numbers greater than 10,00010{,}00010,000 is 96\boxed{96}96​

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