Question 1061878: Tom is planning to leave from Cebu to Manila on Monday morning and has decided that he will take a plane or ship. There are five flights and two ships departing for Cebu that morning. When he returns on Sunday afternoon, he plans to either take a plane or hitch a ride on a helicopter with a friend. There are two flights departing from Cebu to Manila. In how many ways can Tom complete this round trip?
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! 5 flights and 2 ships going gives him 7 ways to get there.
2 flights and 1 helicopter coming home gives him 3 ways to get home.
7 * 3 = 21 ways to get there and back.
assume the flights to get there are f1, f2, f3, f4, f5
assume the ships to get there are s1, s2
assume the flights to get home are f6, f7
assume the helicopter to get home is h1
if he takes f1 to get there, he can take either f6, f7, or h1 to get back.
if he takes f2 to get there, he can take either f6, f7, or h1 to get back.
in other words, for every 1 way to get there, he has 3 possible ways to get back.
do this for all 7 ways to get there and you have a total of 7 * 3 = 21 ways to get there and back.
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