Answer ! the half life of a certain substance is about 4 hours. the graphs shows the decay of a 50 gram sample of the substance that is measured every hour for 9 hours .which function can be used to determine the approximate number of grams of the sample remaining after t hours

Hello.

So you are given the initial amount (50 grams) and two other points on the graph, (1, 42.5) and (4, 26). 

Let's find the exponential function. 


(divide both sides by 50)
(isolate B using the properties of exponents)


This can be rounded to 0.85. 

So therefore, the function that represents the half-life decay is .