Question 1025723
28% reduction is the same as multiplying by .72 , note that 1-.28=.72

.72^2 or .72*.72 = .5184 so 2 hours.

if we waited till the 3rd hour, there would be .373 or 37% well below the 50% level. 


Last, the exact way to calculate a more complex problem is 

.72^N=.5

{{{N=(log.5/log.72)=2.11}}}

So if we believe the body metabolizes to this level of accuracy, the precise answer is 2 hours 6 minutes 36 seconds. Each teacher will have their own requirements for levels of accuracy. It's absurd to see a number like 28% with 2 digits of accuracy, but then produce my answer down to the second, about 5 digits of accuracy. I offer it only to show the precise calculation.