In Colbert’s storage, there are 200 wooden planks / 4 = <<200/4=50>>50 wooden planks.
From his parents, there are 200 wooden planks / 2 = <<200/2=100>>100 wooden planks.
So in total, Colbert has not had to buy 50 wooden planks from storage + 100 wooden planks from his parents + 20 wooden planks from his friends = <<50+100+20=170>>170 wooden planks.
He therefore still needs to buy 200 needed wooden planks – 170 owned wooden planks = <<200-170=30>>30 wooden planks.
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