IXL - Exponential growth and decay: word problems (Algebra 1 practice)

The half-life of a radioactive kind of strontium is 10 hours. How much will be left after 40 hours, if you start with 80 grams of it?

grams

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Learn with an example

question

The half-life of a radioactive kind of nitrogen is 10 minutes. If you start with 120 grams of it, how much will be left after 20 minutes?

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 minutes by the length of a half-life.

2 half-lives have passed.

Now figure out how much nitrogen will be left after 2 half-lives have passed. Multiply the starting amount of nitrogen by

a total of 2 times.

120

That calculation could also be written with exponents:

120

After 2 half-lives, the amount of nitrogen left will be 30 grams.

Looking for more? Try these:

Lesson: Exponential growth

Lesson: Exponential decay

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Not feeling ready yet? These can help:

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Lesson: Exponential growth

Lesson: Exponential decay

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