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10. The number lock of a suitcase has \small 4 wheels, each labelled with ten digits, i.e., from \small 0 to \small 9. The lock opens with a sequence of four digits with no repeats. What is the probability of a person getting the right sequence to open the suitcase?

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Given that each wheel can be labelled with 10 digits,. 

The number of ways of selecting 4 different digits out of the 10 digits = ^{10}\textrm{C}_{4}

These 4 digits can be arranged in their own 4! ways.

\therefore Number of four-digit numbers without repetitions =

^{10}\textrm{C}_{4}\times4! = \frac{10!}{4!.6!}\times4! = 10\times9\times8\times7 = 5040

The number of combination that can open the suitcase = 1

\therefore Required probability of getting the right sequence to open the suitcase =  \frac{1}{5040}

Posted by

HARSH KANKARIA

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