Recurrence Relations - Word Problems
This document covers two main types of recurrence relation word problems: loan repayments and drug dosage calculations. These examples demonstrate the practical applications of recurrence relations in real-world scenarios.
Loan Repayment Problem
The first problem involves a reducing balance loan scenario where Betty borrows £2000 with monthly repayments and interest.
Example: Betty takes out a £2000 loan with 1.5% monthly interest and £450 monthly repayments.
The recurrence relation for the loan balance is derived:
Definition: Bn+1 = 1.015Bn - 450, where Bn is the balance after n months.
The problem is solved step-by-step, showing how the loan balance decreases each month until the final payment in June.
Highlight: The final payment is made in June, with a total repayment of £2086.05.
Drug Dosage Problem
The second problem involves calculating drug levels in a patient's bloodstream using recurrence relations.
Example: A drug with an initial dose of 120ml is administered, with 50% metabolized hourly and 35ml top-ups given each hour.
Two recurrence relations are presented:
- Un+1 = 0.5Un + 35 (drug level after top-up)
- Un+1 = 0.5Un (drug level before top-up)
Vocabulary: Metabolised - The process by which a drug is broken down in the body.
The problem is solved to determine when the drug level falls below the effective threshold of 58ml.
Highlight: The treatment stops being effective between the 3rd and 4th doses when the drug level drops below 58ml.