Combination of Atleast One Thing from n Things When All Are Not Different
The number of...
Question
The number of numbers between 2,000 and 5,000 that can be formed with the digits 0,1,2,3,4 (repetition of digits is not allowed) and are multiple of 3 is?
A
30
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B
48
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C
24
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D
36
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Solution
The correct option is B30 There are 4 places to be filled with the given digits. The thousands place can have only 2, 3 and 4 since the number has to be greater than 2000. For the remaining 3 places, we have pick out digits such that the resultant number is divisible by 3.
The divisibility criteria for 3 states that sum of digits of the number should be divisible by 3.
Case 1: If we pick 2 for thousands place.
The remaining digits we can pick such that sum of digits at all places is a multiple of 3 are:
0,1and3 as 2+1+0+3=6 is divisible by 3.
0,3and4 as 2+3+0+4=9 is divisible by 3.
In both the above combination, the remaining three digits can be arranged in 3! ways. Total number = 2×3!=12
Case 2: If we pick 3 for thousands place.
The remaining digits we can pick such that sum of digits at all places is a multiple of 3 are:
0,1and2 as 3+1+0+2=6 is divisible by 3.
0,2and4 as 3+2+0+4=9 is divisible by 3.
In both the above combination, the remaining three digits can be arranged in 3! ways. Total number = 2×3!=12
Case 3: If we pick 4 for thousands place.
The remaining digits we can pick such that sum of digits at all places is a multiple of 3 are:
0,2and3 as 4+2+0+3=9 is divisible by 3.
In the above combination, the remaining three digits can be arranged in 3! ways. Total number = 3!=6
Total number of numbers between 2000 and 5000 divisible by 3 are 12+12+6=30. Option A is correct.