Question

We are asked to find the number of ways to post 5 letter in 7 letter boxes. It can be done in 7^5 ways . Why not in 5^7 ways?
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Answer 1

Assuming no restrictions- ie, any box can have any number of letters
The first letter can be posted in 7 boxes, so number of ways to post the first letter= 7
The second letter can be posted in 7 boxes, so number of ways to post it = 7
Similarly, number of ways to post the third, fourth, and fifth letter= 7
Therefore, total number of ways to post the letters =7*7*7*7*7=7^5 ways

5^7 ways cannot be used as the above mentioned method is used