4)You count your cells and have 8x10ᶺ5 viable cells/ml you want to see (dilute the cells) to end up with 2x10ᶺ5 viable cells/ml. What volume of cells will you put into 20 ml?

you are diluted them 4 times. So, one part original concentration,three parts solvent.

4 parts in 20 ml
1 part (5ml) original
3 parts (15ml) solvent.

To determine the volume of cells needed to achieve a specific concentration, you can use the formula:

C₁V₁ = C₂V₂

Where:
C₁ = Initial concentration of cells
V₁ = Initial volume of cells
C₂ = Final desired concentration of cells
V₂ = Final desired volume of cells

In this case, you have the following values:
C₁ = 8x10ᶺ5 viable cells/ml
C₂ = 2x10ᶺ5 viable cells/ml
V₂ = 20 ml

Now let's calculate the volume of cells needed (V₁):

C₁V₁ = C₂V₂

V₁ = (C₂V₂) / C₁

Substituting the values:

V₁ = (2x10ᶺ5 viable cells/ml * 20 ml) / 8x10ᶺ5 viable cells/ml

Simplifying the equation:

V₁ = (2 * 20) / 8

V₁ = 40 / 8

V₁ = 5 ml

Therefore, to achieve a concentration of 2x10ᶺ5 viable cells/ml in a final volume of 20 ml, you will need to put 5 ml of cells.