$\"\"$

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(a)

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The equation for radioactive decay is $\"\"$ .

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Where

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$\"\"$ is the number of days the isotope has decayed.

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$\"\"$ is the half-life in days.

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$\"\"$ is remaining isotope.

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Find equation for phosphorous-32.

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The half-life of phosphorous-32 is $\"\"$ days.

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Equation for phosphorous-32 is $\"\"$ .

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Find equation for sulfur-35.

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The half-life of sulfur-35 is $\"\"$ days.

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Equation for sulfur-35 is $\"\"$ .

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$\"\"$

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(b)

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Find value of $\"\"$ .

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Since sulfur-35 have been decaying 5 days longer than phosphorous-32, the equation of radioactive decay is $\"\"$ .

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$\"\"$

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Definition of logarithm : $\"\"$ if and only if $\"\"$ .

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$\"\"$

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The value of $\"\"$ is $\"\"$ .

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$\"\"$

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(a)

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Equation for phosphorous-32 is $\"\"$ .

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Equation for sulfur-35 is $\"\"$ .

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(b)

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The value of $\"\"$ is $\"\"$ .