In Part B of this exercise you will need to make a 1:20 dilution of sheep blood in white cell diluting fluid, to a total of 1 ml.  You need to use 50 μl of sheep blood cells.  How much white cell diluting fluid in μl do you need to use? (You do not need to include units in your answer.)

(Hint: 1 ml is equal to how many μl?)