Three - Digit Numbers
Probability
Level
2
How many three-digit numbers can be formed with the following conditions:
a. all digits are different
b. all digits are arranged in decreasing order
The answer is 120.
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1 solution
Any combination of 3 distinct digits chosen from 0 , 1 , . . . . , 9 can be arranged in decreasing order in precisely one way, so the desired answer is ( 3 1 0 ) = 1 2 0 .