There are 19 cows in a pen, and each cow produces an average of 13 liters of milk per day. How many liters of milk can these cows produce per day?
1个牛栏里有19头牛，每头牛每天平均产奶13升，这些奶牛一天能产奶多少升？
<gadget id="calculator">13 * 19</gadget>
<output>247</output>

<result>247</result>