Question

A number lock on a suitcase has three wheels each labelled with ten digits 0 to 9. If opening of the lock is a particular sequence of three digits with no repeats, how many such sequences will be possible? Also, find the number of unsuccessful attempts to open the lock.

Answer 1

Correct Answer - 720, 719
The first term of the sequence may be anyone of the digits from 0 to 9. So, there are 10 ways of getting the first term.
So, the 2nd and 3rd terms may be obtained in 9 ways and 8 ways respectively.
Required number of sequence `=(10xx9xx8)=720.`
Number of unsuccessful attempts `=(720-1)=719.`