First slide

Introduction to 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 $\frac{6}{24} = \frac{1}{4}$

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