The mass of a radioactive substance follows a continuous exponential decay model, with a decay rate parameter of 1% per day. a sample of this radioactive substance has an initial mass of 2.5kg. find the mass of the sample after five days.

2,38kg

Explanation:

Mass in function of time can be found by the formula: , where is the initial mass, t is the time and k is a constant.

Given that a sample decay 1% per day, that means that after first day you have 99% of mass.

, but , so we have , then

Now using k found we must to find .

explanation:

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the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form