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How many 4 digit numbers are there, with...

How many 4 digit numbers are there, without repetition of digits, If each number is divisible by 5 ?

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To find the number of 4-digit numbers that are divisible by 5 and do not have any repeated digits, we can break the problem down into two cases based on the last digit of the number. ### Step 1: Identify the cases for divisibility by 5 A number is divisible by 5 if its last digit is either 0 or 5. Therefore, we will consider two cases: - Case 1: The last digit is 0. - Case 2: The last digit is 5. ### Step 2: Case 1 - Last digit is 0 If the last digit is 0, the first digit can be any digit from 1 to 9 (since it cannot be 0). This gives us 9 options for the first digit. After choosing the first digit, we have 8 remaining digits to choose from for the second digit, and then 7 remaining digits for the third digit. So, the total number of combinations for this case is: \[ 9 \times 8 \times 7 \] ### Step 3: Case 2 - Last digit is 5 If the last digit is 5, the first digit can be any digit from 1 to 9 (but not 5). This gives us 8 options for the first digit (1-9 excluding 5). The second digit can be any digit from 0 to 9, excluding the first digit and 5, which gives us 8 options. The third digit can be any digit from 0 to 9, excluding the first digit, the second digit, and 5, which gives us 7 options. So, the total number of combinations for this case is: \[ 8 \times 8 \times 7 \] ### Step 4: Calculate the total combinations Now we add the combinations from both cases: \[ \text{Total} = (9 \times 8 \times 7) + (8 \times 8 \times 7) \] Calculating each part: - For Case 1: \[ 9 \times 8 \times 7 = 504 \] - For Case 2: \[ 8 \times 8 \times 7 = 448 \] Adding these together: \[ 504 + 448 = 952 \] ### Final Answer Thus, the total number of 4-digit numbers that are divisible by 5 and do not have repeated digits is **952**. ---
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