A four digit no is formed using 1 2 3 5 with no repetitions then probablity that the no is divisible by 5
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We have four different numbers, and 4 digits to fill the numbers in.
The total number of ways of constructing such 4-digit numbers is 24(or 4P4).
Now, the only way such a 4-digit number is divisible by 5 is if the units digit has 5 in it. This, we can construct such numbers in 6(3P3) different ways.
Probability that the number is divisible by 5 is 6 divided by 24, which is 0.25
Alternate method:
In every number constructed in this manner, it is not difficult to see that each of the 4 given numbers occupy the units digit symmetrically, or equal number of times.
Thus, the probability is 1 divided by 4, which is 0.25
The total number of ways of constructing such 4-digit numbers is 24(or 4P4).
Now, the only way such a 4-digit number is divisible by 5 is if the units digit has 5 in it. This, we can construct such numbers in 6(3P3) different ways.
Probability that the number is divisible by 5 is 6 divided by 24, which is 0.25
Alternate method:
In every number constructed in this manner, it is not difficult to see that each of the 4 given numbers occupy the units digit symmetrically, or equal number of times.
Thus, the probability is 1 divided by 4, which is 0.25
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