## anonymous 5 years ago A radioactive substance decays exponentially. A scientist begins with 130 milligrams of a radioactive substance. After 24 hours, 65 mg of the substance remains. How many milligrams will remain after 45 hours?

1. anonymous

$N(t) = N * .5^{t/h}$ where n(t) is amount of substance left, N = initial amount, t = current time, and h = half-life time. h = 24 hours t= 45 hours, N = 130mg therefore, $N(t) = 130 * .5 ^{45/24} = 35.44mg$

2. anonymous

you are given the half life is 24 hours. so the formula is $A = 130(\frac{1}{2})^{\frac{t}{24}}$ replace t by 45 daniel has it!

3. anonymous

thank you!:)

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