A problem by Sohail Khan
Level
pending
if the post man have four letters and he have to put these in four houses then in how many ways he can put the letters so that no house can get right letter
3
15
9
4
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1 solution
he can put the letters in 9 ways let suppose there are house 1234 and their correct letters are 1234 respectively Now house 1 can get all letters other than letter 1 and same same for others so these are possibilities 2143,2341,2413,3142,3142,3412,3421 and etc