Question 770081: Find the number of different number of 4 digits that can be formed with the digits 1,2,3,4,5,6,7. the digits in any number being all different and the digit in the unit place being always?
Answer by ramkikk66(644)   (Show Source):
You can put this solution on YOUR website!
Digit in the unit place being what? Ok let's assume it is 2. Same logic will work
for any different digit as well.
If the digit at units place is fixed at 2, then to form the rest of the number,
we have to choose 3 digits from a set of 6 (since 2 is already taken).
First digit can be chosen in 6 ways, the 2nd in 5 and the 3rd in 4 ways.
So total number of combinations is 6*5*4 = 120.
Thus, the total number of 4 digit numbers, with each digit being different, and
the unit's digit being fixed, is equal to 120.
Hope you got it:)
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