The capacity of a pool is 1200 liters, it has two inlet pipes A and B and one drain pipe. It will take 9 hours and 10 hours for pipes A and B to fill the pool respectively. There is some water in the pool. If pipe A enters water alone, and the drain pipe drains simultaneously, the water in the pool can be emptied within 3 hours; if pipes A and B enter water together, and the drain pipe drains simultaneously, then the water in the pool can be emptied within 5 hours ． How many liters of water were there originally in the pool?
一个水池的容量是1200升，它有A、B两个进水管和一个排水管．A、B两管单独注满水池分别要9小时和10小时．现水池中存有一部分水．如果A管单独进水，而排水管同时排水，则3小时可把水池中水放空；如果A、B两管一起进水，而排水管同时排水，则5小时可把水池中的存水放空．问水池中原来存有多少升的水？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1_200 / 10 / (2/15)</gadget>
<output>900</output>

<result>900</result>