yass20015 wrote:Thanks Mitch, but I did not get it. Can you please put it with E1,E2,E3,E4 and L1,L2,L3,L4 ? Many thanks!
To my solution above, let's add information about the 4 envelopes.
Let the 4 envelopes be a, b, c and d and the 4 corresponding letters be A, B, C and D.
Let the 4 envelopes be placed on a table in the following order:
a-b-c-d.
Implication:
For every letter to be placed in the correct corresponding envelope, the letters must be arranged in the following order:
ABCD.
Total ways to arrange the 4 letters = 4! = 24.
Write out the ways that ONLY A can be put in the correct position:
ACDB
ADBC
Total ways = 2.
Using the same reasoning, there will be 2 ways that ONLY B can be put in the correct position, 2 ways that ONLY C can be put in the correct position, and 2 ways that ONLY D can be put in the correct position.
Thus, the total number of ways to put EXACTLY 1 letter in the correct position = 2+2+2+2 = 8.
Thus:
P(exactly 1 letter is put in the correct position) = 8/24 = 1/3.
The correct answer is
D.
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