Jack has lego cubes, each of side length 1. He puts them together to form a rectangular prism. If the perimeter of the base of the prism is , what is the height of the prism?
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Let a and b be the lengths of the rectangular base and h be the height of the prism. a , b and h must be positive integers. Then 2 a + 2 b = 1 0 ⇒ a + b = 5 and a b h = 2 2 2 = 2 × 3 × 3 7 . Furthermore, a and b are factors of 2 2 2 that sum to 5 , of which only 2 and 3 work. Thus, these are the lengths of the rectangular base, which allows us to calculate the height as h = 2 × 3 2 × 3 × 3 7 = 3 7 .