<human>:  On Friday, Hank opened his used-bicycle store with a stock of bicycles, all fixed-up and ready to ride. Over the course of the day, he sold 10 bicycles and bought an additional 15 to fix up. On Saturday, he sold 12 bicycles and bought 8 more. And on Sunday, he sold 9 bicycles and bought 11 more. What was the net increase in the number of bicycles in stock in Hank's store over the three days?
<bot>: How many bicycles did Hank sell? ** He sold 10+12+9=<<10+12+9=31>>31 bicycles.
How many bicycles did Hank buy? ** He bought 15+8+11=<<15+8+11=34>>34 bicycles.
What was the net increase in the number of bicycles? ** He now has 34-31=<<34-31=3>>3 more than at Friday's opening.
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