Homework Answers
This is a simple dilution calculation.
The calculation in the question is
one tenth of a milliliter of 10^6 dilution factor gave 31 colonies
Lets translate this into math
1/10 of millilitre is one milliliter /10 = .1 milliliter
.1 milliliter had 31 colonies.
This is from the 10^-6 dilution
.
If .1 milliliter had 31 colonies,
1 milliliter must have 31 * 10 =310 bacteria (each colony counts as one CFU, colony forming unit)
This sample is diluted 10^6 times
This means this sample is 10^6 times more diluted than our actual sample concentration.
The formula is Bacteria * volume/ Dilution
Which is 310 * 1 ml/ 10^-6
so this becomes 310 * 10^6
Exponents change sign when coming to the numerator.
310000000 bacteria/ml are present in the original sample
| 10^-1 | 31000000 |
| 10^-2 | 3100000 |
| 10^-3 | 310000 |
| 10^-4 | 31000 |
| 10^-5 | 3100 |
| 10^-6 | 310 |
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