9. (5 points) A store held a pen promotion, the promotion method was: for every 2 pens bought, 1 small bear toy was given as a gift, no gift for less than 2 pens. The profit from selling 1 pen is 7 yuan, and the purchase price of 1 small bear toy is 2 yuan. This promotion activity made a total profit of 2011 yuan. How many pens did the store sell during this promotion?


【Analysis】According to the problem, the profit from selling 1 pen is 7 yuan, the purchase price of 1 teddy bear toy is 2 yuan, and for every 2 pens sold, 1 teddy bear toy is given as a gift, the profit is $2 \times 7-2=12$ yuan. Let's assume $x$ people bought two pens, then the profit is $12 x$. In addition to the customers who bought two pens, there are also customers who bought only one pen, let's assume $y$ people, we can set up the relationship and solve it by discussing different scenarios.
【Solution】According to the analysis, for every 2 pens sold, 1 teddy bear toy is given as a gift, the profit is $2 \times 7-2=12$ yuan. Let $x$ people bought two pens, then the profit is $12 x$, and $y$ people bought only one pen, the profit is $7 y$, so we have: $12 x+7 y=2011$. Since $x, y$ are non-negative integers, solving this gives: $x=167, y=1$. At this point, the total number of pens sold during the promotion is: $2 x+y=2 \times 167+1=335$ (pens). Therefore, the answer is: 335 pens.