Find how many four digit numbers can be formed by seven digits 1,2,4,5,6,8 and 9 if any digit is selected with repetetion.
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We have 7 digits. From them we have to form four digit numbers. The condition is that we can do the repetition of numbers as we like.
There are four positions for 4 digits in the number.
There are 7 digits for each to be selected.
Number of ways that we can choose 1st digit = 7
Number of ways that we can choose 2nd digit = 7
Number of ways that we can choose 3rd digit = 7
Number of ways that we can choose 4th digit = 7
So total number of ways `= 7^4 = 2401`
So we have 2401 ways to form a four digit number from the set of digits given.
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