Arithmetic Ability
Permutations and Combinations

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Q.

How many 7 digit numbers can be formed using the digits 1, 2, 0, 2, 4, 2, 4?

View Answer

Correct choice: B

Explanation:

There are 7 digits 1, 2, 0, 2, 4, 2, 4 in which 2 occurs 3 times, 4 occurs 2 times. Number of 7 digit numbers = 7!/3!×2! = 420 But out of these 420 numbers, there are some numbers which begin with '0' and they are not 7-digit numbers. The number of such numbers beginning with '0'. =6!/3!×2! = 60 Hence the required number of 7 digits numbers = 420 - 60 = 360
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