Calculating Total Cost

Emma buys 3 notebooks at 4.50 dollars each and 2 pens at 1.75 dollars each. What is her total cost?

Calculate the cost of notebooks: $3 \times 4.50 = 13.50$ dollars = 13.50 dollars for notebooks

Calculate the cost of pens: $2 \times 1.75 = 3.50$ dollars = 3.50 dollars for pens

Add both amounts: $13.50 + 3.50 = 17.00$ dollars = Total: 17.00 dollars

Answer: Emma's total cost is 17.00 dollars.

Making Change

Marcus buys a sandwich for 8.75 dollars and pays with a 20 dollar bill. How much change should he receive?

Identify the operation: Change = Payment - Cost = We need to subtract

Set up the equation: Change $= 20.00 - 8.75$ = Ready to calculate

Calculate the change: $20.00 - 8.75 = 11.25$ = 11.25 dollars change

Answer: Marcus should receive 11.25 dollars in change.

Discount Problem

A jacket originally costs 80 dollars and is on sale for 25% off. What is the sale price?

Calculate the discount amount: $80 \times 0.25 = 20$ dollars = Discount is 20 dollars

Subtract discount from original price: $80 - 20 = 60$ dollars = Sale price: 60 dollars

Alternative method (multiply by remaining %): $80 \times 0.75 = 60$ dollars = Same answer: 60 dollars

Answer: The sale price of the jacket is 60 dollars.

Unit Price Comparison

A 12-pack of juice boxes costs 6.00 dollars. A 20-pack costs 9.00 dollars. Which is the better value?

Find unit price of 12-pack: $6.00 \div 12 = 0.50$ dollars per box = 0.50 dollars each

Find unit price of 20-pack: $9.00 \div 20 = 0.45$ dollars per box = 0.45 dollars each

Compare unit prices: $0.45 < 0.50$ = 20-pack is cheaper per box

Answer: The 20-pack is the better value at 0.45 dollars per box (vs 0.50 dollars per box).

Multi-Step Problem with Tax

Sofia buys a book for 15.00 dollars and a backpack for 35.00 dollars. If sales tax is 8%, what is her total cost including tax?

Find the subtotal: $15.00 + 35.00 = 50.00$ dollars = Subtotal: 50.00 dollars

Calculate the tax: $50.00 \times 0.08 = 4.00$ dollars = Tax: 4.00 dollars

Add tax to subtotal: $50.00 + 4.00 = 54.00$ dollars = Total with tax: 54.00 dollars

Answer: Sofia's total cost including tax is 54.00 dollars.

Mistake: Forgetting to multiply quantity times price

Why: When buying multiple items, students sometimes just add the price once instead of multiplying.

Correct: If you buy 4 items at 3 dollars each, the cost is $4 \times 3 = 12$ dollars, not just 3 dollars.

Mistake: Subtracting discount percentage from price instead of calculating the actual discount

Why: A 20% discount on 50 dollars is not 50 - 20 = 30 dollars.

Correct: First calculate: $50 \times 0.20 = 10$ dollars discount. Then: $50 - 10 = 40$ dollars.

Mistake: Confusing which number to divide when finding unit price

Why: To find price per item, some students divide items by price instead of price by items.

Correct: Unit price = Total price divided by number of items. For 6 dollars for 3 items: $6 \div 3 = 2$ dollars per item.

Mistake: Adding tax before calculating discounts

Why: Tax should be calculated on the final price after any discounts are applied.

Correct: First apply the discount, then calculate tax on the discounted price.

Shopping with a Budget

When shopping with limited money, you need to track your running total to stay within budget.

You have 25 dollars. A shirt costs 12.99 dollars and socks cost 5.49 dollars. Your total is $12.99 + 5.49 = 18.48$ dollars, leaving you $25 - 18.48 = 6.52$ dollars.

Comparing Store Prices

Smart shoppers compare unit prices to find the best deal, especially when packages come in different sizes.

Store A sells 6 apples for 3.00 dollars (0.50 dollars each). Store B sells 8 apples for 3.60 dollars (0.45 dollars each). Store B has the better price per apple.

Restaurant Bills and Tips

When dining out, you need to calculate tips based on the bill amount and sometimes split costs with friends.

A meal costs 32 dollars. A 15% tip is $32 \times 0.15 = 4.80$ dollars. Total with tip: $32 + 4.80 = 36.80$ dollars.

Q: How do I convert a percentage to a decimal for calculations?

A: Divide the percentage by 100. For example, 25% becomes $25 \div 100 = 0.25$. Then multiply by this decimal.

Q: Should I calculate tax before or after a discount?

A: Always apply discounts first, then calculate tax on the discounted price. This gives you the correct final total.

Q: How do I know which size is a better deal?

A: Calculate the unit price (price per item or per unit of measurement) for each size. The lower unit price is the better deal.