## Answers

Here's how you do it.

#### Explanation:

You can see the general method of calculating dilution factors in this Socratic answer.

The general method for calculating serial dilutions is in this answer

The general formula is for calculating a single dilution factor is

Here you have two dilution factors, one for the first dilution and another for the other dilutions.

**First dilution **:

You have diluted the sample by a factor of 20.

The dilution factor is often used as the denominator of a fraction.

Thus, a

**The other dilutions**:

For each step, the dilution factor is 4 or 1:4.

**The Serial Dilutions**

The formula for serial dilutions is

We can generalize this formula as

Thus,