There were 50 cats on a rock. Four boats came and carried away 5 cats each, and later, 3/5 of the remaining cats ran after a mouse they'd seen. How many cats were left on the rock?
When four boats carried away 5 cats each, the total number of cats that left the rock is 4*5 = 
<gadget id="calculator">4*5</gadget>
<output>20</output>
20 cats.
The number of cats remaining on the rock became 50-20 = 
<gadget id="calculator">50-20</gadget>
<output>30</output>
30.
Later 3/5 of the remaining cats left the rock and ran after a mouse, a total of 3/5*30 = 
<gadget id="calculator">3/5*30</gadget>
<output>18</output>
18 cats.
The number of cats that remained on the rock is 30-18 = 
<gadget id="calculator">30-18</gadget>
<output>12</output>
12 cats.

<result>12</result>