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How many ordered triples can you form of 10 items ?
10*9*8 = 720.
How many ordered triples can you form, where Harry occupies the #2 position ?
Obviously, 9*8 = 72
(simply putting someone of remaining 9 persons to position #1 and someone of remaining 8 persons to position #3).
How many ordered triples can you form, where Harry occupies the #3 position ?
Obviously, 9*8 = 72
(using same arguments).
So, your space of all events consists of 720 elements; of them, favorable are 72 + 72 = 144 events.
Therefore, the probability the problem asks for, is = = = 0.2 = 20%. ANSWER