MathIsimple
Lesson 3-4

Decimals & Money Applications

Apply decimal skills to real-world money problems and currency conversion. Master money calculations with shopping, change making, and financial literacy.

Learning Scenario: Money Exchange

Scenario: You're at a store with $10.00 and want to buy items that cost $3.75. How much change will you get back? What if you buy two items: one for $2.50 and another for $4.25? Can you afford both with your $10.00?

This is where decimal skills meet real-world money problems! Understanding how decimals work with money helps you make smart shopping decisions and manage your finances.

Dollar and Cent Conversion

Money uses decimals where the dollar is the whole number part and cents are the decimal part (hundredths).

Conversion:

  • • $1.00 = 100 cents
  • • $0.25 = 25 cents
  • • $0.75 = 75 cents
  • • 150 cents = $1.50
Change Making

To make change, subtract the cost from the amount paid. Use decimal subtraction skills to calculate the difference.

Example:

Paid: $5.00
Cost: $3.75
Change: $1.25

Step-by-Step Learning
1

Understanding Money as Decimals

Money amounts are written as decimals where the dollar sign represents the decimal point. $3.75 means 3 dollars and 75 cents.

Example: $3.75 = 3 dollars + 75 cents = 375 cents total

2

Adding Money Amounts

Add money amounts just like adding decimals. Align the decimal points and add each place value.

Example: $2.50 + $4.25 = $6.75 (2 + 4 = 6 dollars, 50 + 25 = 75 cents)

3

Making Change

To make change, subtract the cost from the amount paid. Use decimal subtraction with proper alignment.

Example: $10.00 - $3.75 = $6.25 (10 dollars - 3 dollars = 7 dollars, but we need to borrow)

Interactive Activities

Activity 1: Shopping Spree

You have $20.00. Can you afford these items?

  • • Book: $8.95
  • • Pen set: $3.50
  • • Notebook: $4.25
  • • Calculator: $12.99
  • • Total cost: ?
  • • Change: ?

Activity 2: Change Making

Calculate change for these purchases:

  • • Paid: $5.00, Cost: $2.75
  • • Paid: $10.00, Cost: $7.50
  • • Paid: $20.00, Cost: $15.25
  • • Paid: $50.00, Cost: $32.80
Practice Problems

Problem Set 1: Money Addition

1. $2.50 + $1.75 = ?

2. $5.25 + $3.80 = ?

3. $8.95 + $4.50 = ?

4. $12.75 + $6.25 = ?

Problem Set 2: Change Making

5. Paid: $10.00, Cost: $7.25, Change: ?

6. Paid: $20.00, Cost: $15.50, Change: ?

7. Paid: $5.00, Cost: $2.85, Change: ?

8. Paid: $50.00, Cost: $32.75, Change: ?

Problem Set 3: Real-World Applications

9. Convert 325 cents to dollars

10. Convert $4.75 to cents

11. Budget: $25.00, Spent: $18.50, Remaining: ?

12. Tip: 15% of $12.00 = ?

Common Mistakes to Avoid

❌ Confusing dollars and cents

Wrong: $3.75 = 375 dollars (confusing cents with dollars)

Correct: $3.75 = 3 dollars and 75 cents = 375 cents total

❌ Forgetting to include the dollar sign

Wrong: Writing 3.75 instead of $3.75

Correct: Always include the dollar sign when writing money amounts

Key Takeaways

Money amounts are written as decimals with dollar signs

1 dollar = 100 cents, so $1.00 = 100 cents

Use decimal addition and subtraction skills for money calculations

Always include the dollar sign when writing money amounts