Is there much of a difference between 99.9% or 99.999%?

Use our present need for cleanliness to engage your students.

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Does it really matter whether you kill 99.9% of the bacteria or 99.999% of the germs?

In this activity, we've asked students to consider whether these claims about these two wipes' efficacy really make a difference.  We've supplied students with a list of bacteria counts on various surfaces and asked them to calculate how much of a difference these two different percents make in wiping out germs.

Begin the activity with a notice and wonder while looking at the wipes.  Then show the kids the list of items without the number of bacteria and have them take some estimates as to which are most and least disgusting in terms of bacteria per square inch.  They will be surprised by some of the numbers! This is also an excellent opportunity to deal with repeating decimals.

The Activity: KillingGerms-2020.pdf

CCSS: 5.NBT.3, 5.NBT.7, 6.NS.3, 7.NS.2.d, 8.NS.1

For members we have an editable Word docx, an Excel sheet with data and calculations, and solutions.

KillingGerms-2020.docx    bacteria-count2020.xlsx    KillingGerms-solution2020.pdf

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