He gave 2*20=$<<2*20=40>>40.
So the total cost was 40-16=$<<40-16=24>>24.
That means each slice costs 24/3=$<<24/3=8>>8.
That means it costs 8*100=<<8*100=800>>800 cents.
So each slice is 800/20=<<800/20=40>>40 cents.
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