Discussion :: Exam Questions Paper
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Given digits 2, 2, 3, 3, 3, 4, 4, 4, 4 how many distinct 4 digit numbers greater than 3000 can be formed?
Answer : Option B
Explanation :
The given digits are 2, 2, 3, 3, 3, 4, 4, 4, 4 we have to find the numbers that are greater than 300
∴ The first digit can be 3 or 4 but not 2.
Now, let us fix the first, second and third digits as 3, 2, 2, then the fourth place can be filled in 3 ways.
∴ The number of ways is 3 similarly, we fix first third and fourth place as 3, 2 and 2 respectively (4) so the second place can be filled in 3 ways again,
The number of ways is 3
Now, we fix first, second and fourth, previous cases and we obtain the same result.
∴ The number of ways is 3 so, the total number of ways is 9 similarly this can done by fixing the numbers as 3 and 4 (instead of 2) and thereby we obtain the a ways each
The number of numbers starting with 3 is 27
Similarly by taking 4 as the first digit we get 27 numbers
∴ The number of numbers that are greater than 3000 is 27 + 27 = 54
But, 3222, 4222, is not possible as there are only two 2's, 3333 is not possible as there are only three 3's
∴ The total number of numbers that are greater than 3000 is 54 - 3 = 51.
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