Xiao Ming goes to the store to buy 66 red and black pens in total. The red pens are priced at 5 yuan each, and the black pens are priced at 9 yuan. Since the quantity purchased is large, the store gives a discount. The red pens are priced at (17/ 20) Pay, the black pen pays according to the price \begin{array}\\4\\\overline{5}\end{array}, if he pays less than the price \begin{array}\\ 9\\\overline{50}\end{array}, how many red pens did he buy?
小明到商店买红黑两种笔共66支，红笔每支定价5元，黑笔每支定价9元，由于买的数量较多，商店就给予了优惠，红笔按定价的(17/20)付钱，黑笔按定价的\begin{array}\\4\\\overline{5}\end{array}付钱，如果他付的钱比按定价少付\begin{array}\\9\\\overline{50}\end{array}，那么他买了红笔多少支？
<gadget id="calculator">5 + 6</gadget>
<output>11</output>

<gadget id="calculator">6 / 11</gadget>
<output>6/11 = around 0.545455</output>

<gadget id="calculator">66 * (6/11)</gadget>
<output>36</output>

<result>36</result>