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

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.

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

expression #3 is not equivalent. the others are.