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A password, which consists of the digits from 0 to 9, and is of length 4 that uses exactly 2 different digits. How many different passwords can there be?

A password, which consists of the digits from 0 to 9, and is of length 4 that uses exactly 2 different digits. How many different passwords can there be?

Grade:11

1 Answers

India VK
42 Points
9 years ago

Choose 2 digits out of 9 in 9C2 ways. Next permute these 2 digits into 4 places - which can be done in 4!/2!2! ways

 

So total number of ways = 9C2. 4!/2!2!

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