<human>:  Mark realizes that a lot of the friends on his friends list are people he doesn't talk to anymore. He keeps 40% of his friends list and then contacts the rest. Of those only 50% respond. He removes everyone who did not respond. If he had 100 friends how many does he have left after the removal?
<bot>: How many friends did Mark contact? ** He contacted 1-.4=<<1-.4=.6>>.6 of his friends
How many friends did Mark contact? ** So he contacted 100*.6=<<100*.6=60>>60 people
How many friends does Mark remove? ** So he removes 60/2=<<60/2=30>>30 people
How many friends does Mark have left? ** So he has 100-30=<<100-30=70>>70 friends left
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