Dattaprabhakar G. answered 09/08/14
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Repeated application of the "m times n" rule: "If a system requires two stages, if the first stage can be completed in m ways and if the second in n ways, then the system can be completed in m times n ways."
Here the "system" (planning your trip) has three stages, countries (4), airlines (3) and hotels 5). You can plan your trip in 4 times 3 times 5 ways. = 60 different ways.
Dr. G.