How many ordered triples of positive integers are there such that ?
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a b c = 6 4
a b c = 2 4 × 3 4
Let a = 2 a 1 × 3 a 2 , b = 2 b 1 × 3 b 2 , c = 2 c 1 × 3 c 2
Then the equation becomes
( 2 a 1 × 3 a 2 ) ( 2 b 1 × 3 b 2 ) ( 2 c 1 × 3 c 2 ) = 2 4 × 3 4
2 a 1 + b 1 + c 1 × 3 a 2 + b 2 + c 2 = 2 4 × 3 4
Then we have
a 1 + b 1 + c 1 = 4
a 2 + b 2 + c 2 = 4
By the technique Stars and Bars ,
The combinations of ( a 1 , b 1 , c 1 ) = ( a 2 , b 2 , c 2 ) = ( 2 6 ) = 1 5
Then, we multiply the arrangements of them to find the total combinations of a 1 , a 2 , b 1 , b 2 , c 1 , c 2 , which is
1 5 2 = 2 2 5