Q. In how many ways 3 letters can be posted in 4 letter-boxes, if all the letters are not posted in the same letter-box?
A) 63
B) 60
C) 77
D) 81
Explanation
(b)
Three letters can be posted in 4 letter boxes in $4^{3} = 64$ ways but it consists the 4 ways that all letters may be posted in same box.
Hence, required number of ways $= 64 - 4 = 60$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.