First slide

Theorems of probability

Question

A four figure number is formed of the figures 1,2,3,5 with no repetitions. The probability that the number is divisible by 5 is

Moderate

A

$\frac{3}{4}$
B

$\frac{1}{4}$
C

$\frac{1}{8}$
D

None of these

Solution

The total number of ways in which four-figure numbers can be formed is $4!$ =24.
A number is divisible by 5 if at unit's place we have 5.
Therefore, unit's place can be filled in one way and the remaining 3 places can be filled with the other digits in $3!$ ways.
Hence, total number of numbers divisible by 5 is $3!$ = 6. So, the required probability is 6/24 =1/4

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