You have a cell suspension for which you need to determine the concentration of cells/ml.  You take 20 μl of cell suspension and this with 60 μl of counting solution.  You perform a haemocytometer count, and you have counted 62, 72, 61, and 68 cells in the four large outer squares (A, B, C, and D) of the haemocytometer.

What is the concentration (in cells/ml) of your sample? (Answer in standard notation (e.g. 62000 instead of 6.2 × 10⁴).)