Question
Question: There are four postcards and five letter boxes. In how many ways postwards can be dropped if all of ...
There are four postcards and five letter boxes. In how many ways postwards can be dropped if all of them are not dropped in the same letter box ?
A
620
B
3120
C
252
D
1020
Answer
620
Explanation
Solution
When there is no restriction, each letter can be dropped in any five of the letter boxes in 5 ways.
∴ Total ways without restriction = 5 x5 x 5 x 5
However in 5 ways all the postcards can be dropped in the same letter box.
∴ Required ways = 54- 5 = 620