A set of 12 encyclopedias is priced at 810 yuan. Uncle Wang wants to buy 5 of them, how much does it cost?
一套12本的百科全书定价810元．王叔叔想买其中的5本，需要多少元？
<gadget id="calculator">810 / 12</gadget>
<output>135/2 = around 67.5</output>

<gadget id="calculator">(135/2) * 5</gadget>
<output>675/2 = around 337.5</output>

<result>675/2 = around 337.5</result>