20 buses are running between two places P and Q. In how many ways can a person go from P to Q and return by a different bus?  Choose the correct option: A) None of these B) 380 C) 312 D) 324 E) 342
Explanation :   He can go in any bus out of the 20 buses.   Hence He can go in 20 ways.   Since he can not come back in the same bus that he used for travelling,   He can return in 19 ways.   Total number of ways = 20 x 19 = 380. Answer : Option 380
<result>B</result>
20 buses are running between two places P and Q. In how many ways can a person go from P to Q and return by a different bus?