A person writes 4 letters and addresses 4 envelopes. If the letters are placed at random in the envelopes, then the probability that all the letters are not placed in the right envelopes is

• 8
the letters can be kept in the envelops in 44 ways . but there is only one way to keep them in right places . so probability that all the letters are not placed in the right envelops =1/ 44
• -7
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