$\"\"$

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(a)

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The amount $\"\"$ of a radioactive material present at time $\"\"$ is $\"\"$ .

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Where $\"\"$ is the original amount of the radioactive material and $\"\"$ is a negative number that presents a rate of decay.

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Find the decay rate of strontium 90.

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The function is $\"\"$ .

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Compare the function with $\"\"$ .

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$\"\"$

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The decay rate of strontium 90 is $\"\"$ per year.

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$\"\"$

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(b)

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The function is $\"\"$ .

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Find the amount of strontium 90 is left after $\"\"$ years.

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Substitute $\"\"$ and $\"\"$ in the function.

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$\"\"$

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The amount of strontium 90 is left after $\"\"$ years is $\"\"$ grams.

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$\"\"$

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(c)

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Find the number of years when the amount of the strontium 90 is left $\"\"$ grams..

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The function is $\"\"$ .

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Substitute $\"\"$ and $\"\"$ in the function.

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$\"\"$

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Take natural logarithm on each side.

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$\"\"$

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The amount of the strontium 90 is left $\"\"$ grams after $\"\"$ years.

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$\"\"$

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(d)

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Find the time to half life of strontium 90.

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The function $\"\"$ .

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Half-life of the function $\"\"$ .

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Substitute $\"\"$ in the function.

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$\"\"$

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$\"\"$

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Take natural logarithm on each side.

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$\"\"$

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Half-life of strontium 90 is $\"\"$ years.

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$\"\"$

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(a) The decay rate of strontium 90 is $\"\"$ per year.

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(b) The amount of strontium 90 is left after $\"\"$ years is $\"\"$ grams.

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(c) The amount of the strontium 90 is left $\"\"$ grams after $\"\"$ years.

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(d) Half-life of strontium 90 is $\"\"$ years.