Question: two pipes running together can fill a cistern in 3 1/13 minutes?
Answer: Let faster pipe takes x min to fill the cistern. To fill the cistern slower pipe take (x+3) min. In 3 1/13= 40/13 min the slower pipe filled the cistern= 40/13 × (1/x+3) = 40/13(x+3). Hence, Faster pipe takes 5 min to fill the cistern while slower pipe takes (x+3) = 5+3= 8 min to fill the cistern.