ctisdale64
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### Trouble getting "21" cups out of Which Filtration Material Leads to the Best Drinking Water

Working on the Science Project and the instructions are unclear. It states that I should prepare a total of "21 cups", but all I can come up with are nine cups. The instructions are unclear, please help. Then later on in the experiment it has a total of "27" cups. Not sure how to come up with 27 cups. So confused by the instructions.

SciB
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### Re: Trouble getting "21" cups out of Which Filtration Material Leads to the Best Drinking Water

Hi,

This is a bit confusing! I'll try to make it clear for you.

Here is the link to your project on testing different carbon filters: https://www.sciencebuddies.org/science- ... #procedure

Here is the procedure for preparing the test solutions and the filters:

In this section, you will prepare a total of 21 cups: 3 cups with different food color solutions, 9 cups with either no carbon, granulated carbon, or powdered carbon (3 of each type), and 9 filtration cups (empty cups with filters attached).

Breaking it down into separate items:

1 c no food color in 2 c of water
1 c + 4 drops food color per 2 c of water
1 c + 10 drops food color per 2 c of water

3 c no carbon (one for each water sample)
3 c granulated carbon
3 c powdered carbon

9 empty cups with coffee filter attached (one for each of the 9 cups of filter material)

That makes a total of 21 cups for this section.
Now the procedure calls for doing three runs for EACH of the three 'pollution' conditions so you need to prepare two more sets of nine cups of filter material. That is where the 27 cups comes from. You also need to prepare 18 more empty cups (27 total) with coffee filters because you will need one filter with cup for each water sample and each filter condition.

3 water samples x 3 filter conditions x three runs = 27 cups of filter material and 27 cups with filters

Be sure to label all the cups BEFORE you start the experiment.

Are you OK with the procedure now? If you still have a question let us know. Once you start doing the set up for the experiment you will see better where the numbers are coming from.

Good luck!

Sybee