A person writes four letters and address four envelopes. If the letters are placed in the envelopes at random, then the probability that not all letters are placed in the right envelope is
- A$\frac{15}{24}$
- B$\frac{11}{24}$
- C$\frac{23}{24}$
- D$\frac{1}{24}$
✓ Correct answer: C
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