Use (9/10) meters of iron wire to make square learning tools, and make 3 (5/7) ones using it. How many meters does each square use on average?
用(9/10)米的铁丝做正方形学具，做3个用了它的(5/7)，平均每个正方形用多少米？
<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">(5/7) / 3</gadget>
<output>5/21 = around 0.238095</output>

<gadget id="calculator">(9/10) * (5/21)</gadget>
<output>3/14 = around 0.214286</output>

<result>3/14 = around 0.214286</result>