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Ratio, rate and proportion

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Apuntes de la lección

What is a Ratio?

  • A ratio compares two numbers or amounts. It tells you how much of one thing there is compared to another.
  • For example, if a bowl has 8 oranges and 6 lemons, the ratio of oranges to lemons is 8 to 6.
  • You can write a ratio in three ways: using the word "to" (8 to 6), using a colon (8:6), or as a fraction (8/6).
  • The order matters! The ratio of oranges to lemons is 8:6, but the ratio of lemons to oranges is 6:8.
  • A ratio can compare parts to parts (oranges to lemons) or parts to the whole (oranges to total fruit).

Simplifying Ratios

  • You can simplify a ratio just like you simplify a fraction.
  • To simplify, divide both numbers by the same number (a common factor).
  • For example, 8:6 can be simplified by dividing both numbers by 2, giving 4:3.
  • A ratio is in simplest form when the only common factor of the two numbers is 1.
  • Simplifying does not change the ratio's meaning; 8:6 and 4:3 are equivalent ratios.

Equivalent Ratios and Ratio Tables

  • Equivalent ratios are ratios that show the same comparison, like 2:3 and 4:6.
  • You can find equivalent ratios by multiplying or dividing both numbers by the same number.
  • A ratio table is a table that lists equivalent ratios. It helps you solve problems.
  • For example, if a recipe uses 2 cups of flour for 3 cups of sugar, you can make a table: 2:3, 4:6, 6:9, and so on.
  • Ratio tables help you find missing numbers in a proportion.

Sharing a Quantity in a Given Ratio

  • Sometimes you need to share an amount in a given ratio, like sharing $20 in the ratio 2:3.
  • First, add the parts of the ratio: 2 + 3 = 5 parts.
  • Then divide the total by the number of parts: $20 ÷ 5 = $4 per part.
  • Multiply each part by the value of one part: 2 × $4 = $8 and 3 × $4 = $12.
  • Check: $8 + $12 = $20, so the sharing is correct.

Rates and Unit Rates

  • A rate is a ratio that compares two quantities with different units, like miles per hour or dollars per pound.
  • A unit rate is a rate where the second quantity is 1. For example, 60 miles per hour means 60 miles in 1 hour.
  • To find a unit rate, divide the first quantity by the second quantity.
  • For example, if a car travels 120 miles in 2 hours, the unit rate is 120 ÷ 2 = 60 miles per hour.
  • Unit price is a unit rate for cost, like $2 per apple. It helps you compare prices.

Comparing Rates and Finding Better Value

  • To find the better value, compare unit prices.
  • For example, a 12-ounce box of cereal costs $3, and a 20-ounce box costs $4.50.
  • Find the unit price for each: $3 ÷ 12 = $0.25 per ounce, and $4.50 ÷ 20 = $0.225 per ounce.
  • The 20-ounce box has a lower unit price, so it is the better value.
  • Always check the units so you compare the same thing.

Proportions

  • A proportion is an equation that says two ratios are equal, like 6:8 = 3:4.
  • You can write a proportion as a fraction: 6/8 = 3/4.
  • In a proportion, the cross products are equal: 6 × 4 = 8 × 3.
  • You can use cross multiplication to solve for a missing number in a proportion.
  • For example, if 2/3 = x/9, then 2 × 9 = 3 × x, so 18 = 3x, and x = 6.

Using Ratios in Real Life

  • Ratios are used in recipes to keep ingredients in the right amounts.
  • Maps use ratios (scale) to show real distances. For example, 1 inch on a map might mean 10 miles in real life.
  • Speed is a rate: distance divided by time, like 60 miles per hour.
  • Double number lines and tape diagrams are tools to visualize ratios and solve problems.
  • Understanding ratios helps you solve many everyday problems, from shopping to cooking.

Diapositivas

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Preguntas de práctica

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  1. 1.What does the ratio 3:2 mean?

    Easy
    • A3 parts of one thing to 2 parts of another
    • B3 plus 2 equals 5
    • C3 divided by 2 equals 1.5
    • D3 times 2 equals 6
  2. 2.The ratio 8:6 is equivalent to 4:3.

    Easy

    True or false?

  3. 3.Which of the following is the same as the ratio 10:15?

    Easy
    • A2:3
    • B3:2
    • C5:10
    • D10:5
  4. 4.Which of the following are equivalent to the ratio 2:3? (Select all that apply)

    Easy
    • A4:6
    • B6:9
    • C3:2
    • D1:1.5
    • E10:15
  5. 5.A recipe needs flour and sugar in the ratio 3:1. If you use 9 cups of flour, how many cups of sugar do you need?

    Medium
    • A3
    • B6
    • C9
    • D27
  6. 6.Which is the better buy: 6 apples for $3 or 10 apples for $4?

    Medium
    • A6 apples for $3
    • B10 apples for $4
    • CThey are the same price per apple
    • DCannot tell from the information
  7. 7.Match each ratio to its simplified form.

    Medium
    • 4:8
    • 9:12
    • 15:20
    • 1:2
    • 3:4
    • 3:4
  8. 8.Put these steps in order to solve: 'Share 20 sweets in the ratio 2:3.'

    Medium
    • Add the parts of the ratio: 2 + 3 = 5.
    • Divide the total by the sum: 20 ÷ 5 = 4.
    • Multiply each part by 4: 2×4 = 8 and 3×4 = 12.
    • Check: 8 + 12 = 20.

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