1/2 Life and Finding Exponential Equations

Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?

• 0.25g
• 2.5g
• 25g
• 80g

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CCSS.HSF.LE.A.4

The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?

• 100.0g
• 50.0g
• 12.5g
• 8.5g

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CCSS.HSF.LE.A.4

If the half-life of uranium-232 is 70 years, how many half-lives will it take for 10 g of it to be reduced to 1.25 g?

• 1 half-life
• 2 half-lives
• 3 half-lives
• 4 half-lives

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CCSS.HSF.LE.A.4

After the third half-life, how much of the sample is left?

• 1/2
• 1/3
• 1/16
• 1/8

Iodine-131 has a half life of 8 days. A sample starts with 3000 radioactive nuclei. How many days will it take to have 94 nuclei left?

Hint you have to half a few times, but remember how long it takes to half!

• 32 days

• 40 days

• 375 days

• 16 days

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CCSS.HSF.LE.A.4

After 64 days the activity of a radioactive nuclide has fallen to one sixteenth of its original value. The half-life of the radioactive nuclide is

• 2 days.

• 4 days.

• 8 days.

• 16 days.

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CCSS.HSF.LE.A.4

If 10 mg of iodine 131 is given to a patient, how much is left after 24 days? The half-life of iodine-131 is 8 days.

• 1.25mg
• 1.25g
• 10g
• 10mg

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CCSS.HSF.LE.A.4

After 22,800 years, approximately what percentage of the original carbon-14 remains?

• 15%

• 12.5%

• 6.25%

• 3.125%

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CCSS.HSF.LE.A.4

Which is the basic form of an exponential function?

The half-life of ibuprofen is 1-hour. You take 400 mg of ibuprofen. Write an exponential equation that could be used to find the amount of ibuprofen you have remaining in your body after x hours.

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CCSS.HSF.LE.A.2