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24 June, 20:49

an element with mass 670 grams decays by 21.8% per minute how much time is remaining after 15 minutes

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Answers (2)
  1. 24 June, 21:01
    0
    After 15 minutes 16.75 g are remaining

    Step-by-step explanation:

    After each minute, the amount remaining is 100 - 21.8 = 78.2% = 0.782 times as much as was present at the start of the minute. So after 1 minute there is 670*0.782 = 523.94 g. After 2 minutes there is 523.94*0.782 = 409.72 g, which is equivalent to 670*0.782^2. Then the general formula is:

    m = 670*0.782^t

    where m is the mass remaining (in grams) and t the time elapsed (in minutes)

    After 15 minutes:

    m = 670*0.782^15 = 16.75 g
  2. 24 June, 21:03
    0
    16.75622173 grams.

    Step-by-step explanation:

    21.8% + 78.2% = 100%

    There is 78.2% of the original remaining each minute.

    670g * 0.782^15

    It's to the power of 15 because it's done 15 times.

    16.75622173 grams are remaining.
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