An adult takes 400 mg of ibuprofen. Every two hours, the amount of ibuprofen in the person's system decreases by 29%. How much will be left after 10 hours?

400 * (1-.29)^5 = 72.17

To find out how much ibuprofen will be left after 10 hours, we can use the concept of exponential decay.

First, we need to calculate the amount of ibuprofen remaining after each 2-hour interval. To do this, we multiply the previous amount by (100% - 29%) or 0.71 (since 29% is equivalent to 0.29):

Amount after 2 hours = 400 mg * 0.71 = 284 mg
Amount after 4 hours = 284 mg * 0.71 = 202 mg
Amount after 6 hours = 202 mg * 0.71 = 144 mg
Amount after 8 hours = 144 mg * 0.71 = 103 mg
Amount after 10 hours = 103 mg * 0.71 = 73 mg

Therefore, after 10 hours, approximately 73 mg of ibuprofen will be remaining in the person's system.