IXL - Half-life: word problems (Algebra 1 practice)

You have 64 grams of a radioactive kind of sodium. How much will be left after 9 years if its half-life is 3 years?

grams

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question

You have 80 grams of a radioactive kind of tellurium. How much will be left after 8 months if its half-life is 2 months?

grams

key idea

A half-life is the amount of time it takes for half of a radioactive substance to turn into something else. For each half-life, multiply the amount of radioactive substance by

solution

First, find out how many half-lives have passed. Divide the number of months by the length of a half-life.

4 half-lives have passed.

Now figure out how much tellurium will be left after 4 half-lives have passed. Multiply the starting amount of tellurium by

a total of 4 times.

That calculation could also be written with exponents:

After 4 half-lives, the amount of tellurium left will be 5 grams.

Looking for more? Try these:

Lesson: Exponential decay

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Not feeling ready yet? These can help:

V.1Evaluate an exponential function

L.3Multiply fractions by whole numbers: word problems

Lesson: Exponential decay

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