When a large municipal water tank is empty, it takes a Type JQ pump, working alone, 72 hours to fill the tank, whereas as Type JT pump, working alone, would take only 18 hours to fill the tank completely. If the tank starts at half full, how long would it take two Type JQ pumps and a Type JT pump, all three pumps working together, to fill the tank?

Answer: 6 hoursStep-by-step explanation:Given : Time taken by Type JQ pump to fill the tank = 72 hoursThen , Time taken by Type JQ pump to fill half of the tank = 36 hoursTime taken by Type JT pump to fill the tank = 18 hoursThen, Time taken by Type JT pump to fill the tank = 9 hoursNow, if he tank starts at half full then the time taken by two Type JQ pumps and a Type JT pump all three pumps working together to fill the tank :-[tex]\dfrac{1}{t}=\dfrac{1}{36}+\dfrac{1}{36}+\dfrac{1}{9}\\\\\Rightarrow\dfrac{1}{t}=\dfrac{1+1+4}{36}=\dfrac{1}{6}\\\\\Rightarrow t=6[/tex]Hence, it will take 6 hours to fill the tank.