Answer:
2.37×10^-11 milliliters
Step-by-step explanation:
The exponential model for decay is ...
y = a·b^x
where 'a' is the initial value, 'b' is the decay factor, and x is the number of intervals over which the decay is taking place.
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Here, you're given an initial value of a=500 mL.
The decay factor is 1 more than the decay rate, so is ...
b = 1 -12% = 0.88
We are asked for the remaining amount after 240 intervals (breaths), so that will be ...
y = 500·0.88^x
y = 500·0.88^240 ≈ 2.37×10^-11 . . . . milliliters
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Additional comment
That's about 640 million molecules of air--not very much. After 400 breaths, there is about 1 molecule of the original air remaining.
