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How many different numbers can be formed from the digits 3, 4, 5, 6 and 7 when repetitions are allowed?

3125
625
3905
125

Correct Answer: 3905

Explanation:

Number of 1 digit numbers = 5
Number of 2 digit numbers = 5² = 25
Number of 3 digit numbers = 5³ = 125
Number of 4 digit numbers = 5⁴ = 625
Number of 5 digit numbers = 5⁵ = 3125
∴ Total number of numbers formed with these digits
= 5 + 25 + 125 + 625 + 3125 = 3905

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