Question
From the digits 2, 3, 4, 5, 6 and 7, how many 5-digit numbers can be formed that have distinct digits and are multiples of 12?
CAT 2021
Correct option is
Explanatory Answer :
Any multiple of 12 must be a multiple of both 4 and 3.
First, let us look at the constraint for a number being a multiple of 3. Sum of the digits should be a multiple of 3. Sum of all numbers from 2 to 7 is 27.
So, if we have to drop a digit and still retain a multiple of 3, we should drop either 3 or 6.
So, the possible 5 digits are 2, 4, 5, 6, 7 or 2, 3, 4, 5, 7. when the digits are 2, 4, 5, 6, 7.
the last two digits possible for the number to be a multiple of 4 are 24, 64, 52, 72, 56, 76.
For each of these combinations, there are 6 different numbers possible. So, with this set of 5 digits we can have 36 different numbers.
When the digits are 2, 3, 4, 5, 7. The last two digits possible for the number to be a multiple of 4 are 32, 52, 72, 24.
For each of these combinations, there are 6 different numbers possible. So, with this set of 5 digits we can have 24 different numbers.
Thus a total of 60 such numbers can be formed.
