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Question
How many two-digit numbers can be formed using 1, 2, 3, 4, 5 without repetition of digits?
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Solution
The given digits are 1, 2, 3, 4, 5
A two digit number has unit place and 10’s place.
We are given 5 digits (1, 2, 3, 4, 5).
The unit place can be filled (using the 5 digits) in 5 ways.
After filling the unit place since repetition is not allowed one number (filled in the unit place) should be excluded.
So the 10’s place can be filled (using the remaining 4 digits) in 4 ways
∴ Unit place and 10’s place together can be filled in 5 × 4 = 20 ways.
So the number of two-digit numbers = 20
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