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

How much of a radioactive kind of bismuth will be left after 4 minutes if the half-life is 2 minutes and you start with 40 grams?

grams

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Learn with an example

question

The half-life of a radioactive kind of tin is 10 days. If you start with 160 grams of it, how much will be left after 40 days?

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 days by the length of a half-life.

4 half-lives have passed.

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

a total of 4 times.

160

That calculation could also be written with exponents:

160

After 4 half-lives, the amount of tin left will be 10 grams.

Looking for more? Try these:

Lesson: Exponential decay

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Lesson: Exponential decay

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