Andrew’s guest bedroom took 8 - 2 = <<8-2=6>>6 wooden planks.
His hallways took 2 * 4 = <<2*4=8>>8 planks.
In two bedrooms, he ruined 3 planks each, so the bedrooms took an extra 3 * 2 = <<3*2=6>>6 planks.
In all, he used 8 + 20 + 11 + 6 + 8 + 6 = <<8+20+11+6+8+6=59>>59 planks for his whole house.
Andrew had 6 leftover planks, so he bought 59 + 6 = <<6+59=65>>65 wooden planks to start with.
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