When two numbers are multiplied, one factor is multiplied by 2 and the other factor is reduced by 4. The product becomes 7.8. What is the original product?
两数相乘，一个因数扩大2倍，另一个因数缩小4倍，积变成7.8，原来的积是多少．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">7.8 * 2</gadget>
<output>15.6</output>

<result>15.6</result>