A reference liquid of known viscosity coefficient eta R flows in a horizontal pipe of constant  

cross-section and opens at one end. The pressure difference between the ends of the pipe 

is kept constant. At the open end, a liquid leakage of 3 l in 200 s is measured. Later,  

a liquid with unknown viscosity coefficient eta is allowed to flow into the same tube with  

 the same pressure difference between the tubes ends. A liquid leakage of 0.5 l in 400 s is 

measured. What is the ratio eta /eta R?