Hello Shuvo Saha

You will have to use two formulae.

Formula No1:

Number of cells x desired MOI = total PFU (Plaque Forming Units) needed.

So, in your case

2 x10^7 cells x 5 pfu/cell = 10 x 10^7 (Total PFU desired)

Then, use Formula No 2:

(Total PFU desired) / (PFU/ml) = total ml of virus needed to reach your desired dose.

So, in your case

10 x 10^7 (Total PFU desired) / 5 x10^10 pfu/ml = 2 x 10^-3 = 0.002ml or 2ul.

Add 2.0ul of the stock to the tissue culture flask containing 2 x10^7 cells and label it as 5 MOI.

Best.

thanks a lot