A cistern has been filled with 50 tons. If 20 tons of water are used during the day and 15 tons of water is taken in at night, how many days can the water in the pool be used up?
一个蓄水池，已装满50吨，如果白天用水20吨，晚上进水15吨，多少天可以把水池的水用完．
<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">50 / 5</gadget>
<output>10</output>

<result>10</result>