-- 3 bakers produce 15 cakes in 60 minutes.
-- Each baker produces 15/3 = 5 cakes in 60 minutes.
-- Each baker takes 60/5 = 12 minutes to produce 1 cake.
-- 6 bakers can produce 6 cakes in 12 minutes.
-- 20 cakes will take 20/6 = (3 and 1/3) as much time as 6 cakes.
-- (3 and 1/3) times 12 minutes = 40 minutes.
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An easier way to do it:
-- 3 bakers produce 15 cakes in 60 minutes.
-- 6 bakers could produce 30cakes in 60 minutes.
-- Only 20 cakes are needed. That's only (20/30) = 2/3 of 30 cakes.
-- So it will only take them 2/3 of 60 minutes = 40 minutes to make them.
