Tom needs to lower a rope down 6 stories.   One story is 10 feet.  The only rope being sold is 20 feet long but you lose 25% when lashing them together.  How many pieces of rope will he need to buy?
He needs 10*6=<<10*6=60>>60 feet
He loses 20*.25=<<20*.25=5>>5 feet each time
So he gets 20-5=<<20-5=15>>15 feet from each piece
That means he needs 60/15=<<60/15=4>>4 pieces of rope
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