- A36
- B60
- C72
- D48
View written solutionFree
Correct answer: B
- Divisibility rule for 11
For a 6-digit number with digits , the number is divisible by if
is a multiple of .
Here the digits used are exactly once each.
- Total sum of all digits
Let the sum of digits in odd positions be and in even positions be . Then
and divisibility by requires
Since both are sums of three of the given digits, the difference cannot be . Also, because is even, must be even, so it cannot be . Hence the only possibility is
So we need to split the 6 digits into two groups of 3 each, each summing to .
- Find 3-digit subsets with sum 12
From , the 3-element subsets summing to are:
These are complementary, so one must occupy the odd positions and the other the even positions.
Thus there are 2 ways to choose which set goes to odd positions:
- odd positions: , even positions:
- odd positions: , even positions:
- Arrange digits in positions, respecting first digit nonzero
We now count arrangements for each case.
Case 1: Odd positions get , even positions get
Odd positions are . Since the first digit cannot be , among the arrangements of in odd positions, those with at position 1 are invalid.
If is fixed at position 1, the remaining two digits can be arranged in ways. So valid arrangements for odd positions:
Even positions can be filled with in
ways.
Hence total for Case 1:
Case 2: Odd positions get , even positions get
Now the first digit is one of , so no restriction from leading zero.
Odd positions can be arranged in
ways.
Even positions can be arranged in
ways.
Hence total for Case 2:
- Total count
Therefore, the number of such 6-digit numbers is
So the correct option is B.
More from Permutations and Combinations
- Suppose that 20 pillars of the same height have been erected along the boundary of a circular stadium. If the top of each pillar has been connected by beams with the top of all its non-adjacent pillars, then the total number of beams is :2019 · MCQ
- If then K is equal to :2019 · MCQ
- The number of ways of choosing 10 objects out of 31 objects of which 10 are identical and the remaining 21 are distinct, is :2019 · MCQ
- A group of students comprises of 5 boys and n girls. If the number of ways, in which a team of 3 students can randomly be selected from this group such that there is at least one boy and at least one girl in each team, is 1750, then n is…2019 · MCQ
- Consider three boxes, each containing, 10 balls labelled 1, 2, … , 10. Suppose one ball is randomly drawn from each of the boxes. Denote by ni, the label of the ball drawn from the ith box, (i = 1, 2, 3). Then, the number of ways in which…2019 · MCQ
- There are m men and two women participating in a chess tournament. Each participant plays two games with every other participant. If the number of games played by the men between themselves exceeds the number of games played between the…2019 · MCQ
- n digit numbers are formed using only three digits 2, 5 and 7. The smallest value of n for which 900 such distinct numbers can be formed, is :2018 · MCQ
- The number of four letter words that can be formed using the letters of the word BARRACK is :2018 · MCQ