Unit 8: Problem Solving · Lesson 7
Problem Solving - Lesson 7
What this lesson is for
- Students will understand and practice Problem Solving - Lesson 7
- Students will solve problems related to this topic
Train up a child in the way he should go: and when he is old, he will not depart from it.
Proverbs 22:6
Financial mathematics applies algebraic formulas to real-world money management — one of the most immediately practical mathematics topics in the high school curriculum. Simple interest: I = Prt, where P = principal, r = annual interest rate (as decimal), t = time in years. Total amount: A = P + I = P(1 + rt). Example: $2,500 invested at 4.5% simple interest for 3 years earns I = 2500(0.045)(3) = $337.50; total A = $2,837.50.
Compound interest: A = P(1 + r/n)^(nt), where n = number of compounding periods per year. Compare compounding frequencies for $5,000 at 6% for 10 years: annually (n=1): A = 5000(1.06)^10 ≈ $8,954; quarterly (n=4): A = 5000(1.015)^40 ≈ $9,070; monthly (n=12): A = 5000(1.005)^120 ≈ $9,097; daily (n=365): A ≈ $9,110. Continuous compounding (the limit as n→∞): A = Pe^(rt) ≈ $9,111. More frequent compounding yields more interest, but with diminishing returns. APR (Annual Percentage Rate) is the stated rate; APY (Annual Percentage Yield) accounts for compounding and is what you actually earn — for 6% compounded monthly, APY = (1 + 0.06/12)^12 − 1 ≈ 6.168%.
Credit card debt: understand that high-interest debt compounds against you. $3,000 on a credit card at 24% APR compounded monthly: monthly rate = 2%. If you make no payments, after one year: A = 3000(1.02)^12 ≈ $3,804. After five years: $9,850. The Rule of 72: divide 72 by the interest rate to estimate how long it takes an investment to double (at 6%, doubles in about 12 years; at 12%, about 6 years). Activity: solve fifteen financial problems including simple interest, compound interest (all four compounding frequencies), APY calculations, and debt growth scenarios. Calculate how much more compound interest earns over simple interest for the same principal, rate, and term.
Proverbs 21:5 instructs, "The thoughts of the diligent tend only to plenteousness; but of every one that is hasty only to want." Compound interest rewards patience; debt punishes it. The mathematics of finance is one of the most important practical applications of algebra — and one of the most directly connected to the Biblical values of diligence, stewardship, and avoiding the bondage of debt (Proverbs 22:7: "the borrower is servant to the lender"). Every student should leave high school understanding these calculations well enough to make sound financial decisions.
Guided practice
A farmer invests $2,000 in a savings account at 4% annual interest for 3 years. How much interest is earned? (Use I = Prt)
Show the steps and the answer
1) Formula: I = Prt. 2) Identify: P = $2000, r = 0.04, t = 3. 3) Substitute: I = 2000 × 0.04 × 3. 4) Calculate: I = $240
Answer: 240
A young adult deposits $5,000 at 3% annual interest. How much money will they have after 5 years? (Use A = P + I = P(1 + rt))
Show the steps and the answer
1) Formula: A = P(1 + rt). 2) Identify: P = $5000, r = 0.03, t = 5. 3) Substitute: A = 5000(1 + 0.03 × 5). 4) Calculate: A = 5000(1.15) = $5750
Answer: 5750
How long will it take $8,000 to earn $960 in interest at 6% annual interest? (Use I = Prt, solve for t)
Show the steps and the answer
1) Formula: 960 = 8000 × 0.06 × t. 2) Simplify: 960 = 480t. 3) Solve: t = 960/480. 4) Calculate: t = 2 years
Answer: 2
Homework
Complete the practice problems for Problem Solving - Lesson 7.
Note for the parent
Today's lesson covers Problem Solving - Lesson 7. Estimated time: 55 minutes. Encourage independent work but be available for questions.
The first three of this lesson's 10 questions
Simple interest is calculated as I = Prt, where P = principal, r = annual rate, t = time in years. The formula for total amount A =
Show the answer
Answer: A = P(1 + rt)
$2500 at 4.5% simple interest for 3 years earns I = 2500 * 0.045 * 3 =
Show the answer
Answer: $337.50
Compound interest formula: A = P(1 + r/n)^(nt). Here 'n' is the number of:
Show the answer
Answer: Compounding periods per year
Another 7 questions follow in the lesson itself, each one graded the moment it is answered.