The product of two factors is 820, one of the factors is multiplied by 5, and the other factor remains unchanged, what is the product.
两个因数的积为820，其中一个因数乘5，另一个因数不变，积为多少．
<gadget id="calculator">820 * 5</gadget>
<output>4_100</output>

<result>4_100</result>