A medical researcher, Dr. Varma, monitors the concentration of a radioactive isotope, C C\,C mg/L, in a patient's bloodstream. She believes the concentration decays exponentially over time, where h h\,h is the number of hours after the initial injection. Dr. Varma models the concentration using the formula
C=p×qh C = p \times q^{h} C=p×qhwhere p p\,p and q q\,q are constants.
She plots a graph of log10C\log_{10} Clog10C against h h\,h and determines the equation of the line of best fit to be:
log10C=−0.065h+0.845 \log_{10} C = -0.065h + 0.845 log10C=−0.065h+0.845(i) Show that, correct to three significant figures, p=7.00p = 7.00p=7.00.
(ii) Find the value of qqq, giving your answer to three significant figures.
According to the model, state the hourly percentage decrease in the isotope concentration.
(i) Use the model to predict the isotope concentration 24 hours after the injection.
(ii) Explain why the prediction made in part (c)(i) may be unreliable.
Practise Edexcel A Level Maths Regression, Correlation and Hypothesis Testing with exam-style questions for A Level Maths. 202 questions covering Exponential Models, Measuring Correlation, and Hypothesis Testing for Zero Correlation, 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.
