Every donut costs him $.2 because 2.4 divided by 12 equals <<2.4/12=.2>>.2
So he makes $.8 for every donut he sells because $1 minus $.2 equals .8
He needs to sell 120 donuts because 96 divided by .8 equals <<96/.8=120>>120.
He needs to buy and sell 10 dozen donuts because 120 divided by 12 equals <<120/12=10>>10
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