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number of ways in which eight digit numb...

number of ways in which eight digit number can be formed using the digits from 1 to 9 without repetition, if first four places of the numbers are in increasing order and last 4 places are in decreasing order , is 'n' then `n/70` is equal to.

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To solve the problem of forming an eight-digit number using the digits from 1 to 9 without repetition, where the first four digits are in increasing order and the last four digits are in decreasing order, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding the Selection of Digits**: We need to select 4 digits from the available 9 digits (1 to 9) for the first half of the number, which will be in increasing order. The remaining 5 digits will then be used for the last half of the number, which will be in decreasing order. 2. **Choosing the First Four Digits**: The number of ways to choose 4 digits from 9 is given by the combination formula: \[ \binom{9}{4} \] This represents the number of ways to select 4 digits from 9. 3. **Choosing the Last Four Digits**: After selecting the first 4 digits, we have 5 digits left. We need to choose 4 digits from these remaining 5 for the last half of the number. The number of ways to do this is: \[ \binom{5}{4} \] Since we are choosing 4 out of 5, this is equivalent to simply selecting the one digit that will not be included. 4. **Calculating the Total Combinations**: The total number of ways to form the eight-digit number is the product of the combinations calculated in steps 2 and 3: \[ n = \binom{9}{4} \times \binom{5}{4} \] 5. **Calculating the Combinations**: - Calculate \(\binom{9}{4}\): \[ \binom{9}{4} = \frac{9!}{4!(9-4)!} = \frac{9 \times 8 \times 7 \times 6}{4 \times 3 \times 2 \times 1} = 126 \] - Calculate \(\binom{5}{4}\): \[ \binom{5}{4} = 5 \] 6. **Final Calculation of \(n\)**: Now, substituting the values back into the equation for \(n\): \[ n = 126 \times 5 = 630 \] 7. **Finding \(n/70\)**: Finally, we need to calculate \(n/70\): \[ \frac{n}{70} = \frac{630}{70} = 9 \] ### Final Answer: Thus, the value of \(n/70\) is **9**.
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Knowledge Check

  • Four digit numbers are formed using the digits 0, 2, 3,5 without repetition. The probability of such a number divisible by 5 is

    A
    `1/5`
    B
    `4/5`
    C
    `1/30`
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    2664
    B
    3882
    C
    4044
    D
    4444
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    A
    69
    B
    96
    C
    169
    D
    98
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