The concentration of a drug (C C\,C mg/L) in a patient's bloodstream t t\,t hours after administration is recorded in the table below.
| ttt | 1 | 2 | 4 | 6 | 8 | 10 |
| CCC | 26.3 | 19.1 | 10.0 | 5.2 | 2.8 | 1.4 |
The data is coded using the changes of variable x=tx = tx=t and y=log10Cy = \log_{10} Cy=log10C.
The regression line of y y\,y on x x\,x is found to be y=1.56−0.14xy = 1.56 - 0.14xy=1.56−0.14x.
Given that the data can be modelled by an equation in the form C=abtC = ab^tC=abt where a a\,a and b b\,b are constants, find the values of a a\,a and b b\,b to 3 significant figures.
Give an interpretation of the constant a a\,a in this equation.
Explain why this model might not be reliable for calculating the concentration after 72 hours.
Practise Edexcel A Level Maths Exponential Models with exam-style questions for A Level Maths. 42 questions, matched to the Edexcel A Level Maths (9MA0) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
