here are 4 letters and 4 addressed envelopes. If each letter is randomly placed in an envelope, then in how many ways can wrong choices be made?Choices:- 4^3 4! – 1 16 44-1
Question
here are 4 letters and 4 addressed envelopes. If each letter is randomly placed in an envelope, then in how many ways can wrong choices be made?Choices:- 4^3 4! – 1 16 44-1
Solution
The problem is a classic problem of derangements, also known as the "hat-check problem". It asks for the number of permutations of the letters such that no letter appears in its original position.
The number of derangements of n objects is usually denoted by !n. There is a recursive formula for calculating derangements:
!n = (n-1)(!(n-1) + !(n-2))
For n=4, we have:
!4 = (4-1)(!(4-1) + !(4-2)) = 3(!(3) + !(2))
We know that !2 = 1 and !3 = 2, so we substitute these values in:
!4 = 3(2 + 1) = 9
So, there are 9 ways to make wrong choices. However, this option is not given in the choices. There might be a mistake in the problem or the given choices.
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