Grade 8 Pre-Algebra Rates, Ratios, and Proportions

Grade 8 Pre-AlgebraRates, Ratios, and Proportions CONFIDENTIAL

Warm Up Factor each trinomialby guess and check: 1) 2c - 5 = c + 4 1) c = 9 2) r = 1 2) 8r + 4 = 10 + 2r 3) x = 12 3) 2x -1 = x + 11 4) 28 - 0.3y = 0.7y - 12 4) y = 40 CONFIDENTIAL

Rates, Ratios, and Proportions A ratio is a comparison of two quantities by division. The ratio of a to b can be written a:b or a , b where b ≠ 0. Ratios that name the same comparison are said to be equivalent. A statement that two ratios are equivalent, such as 1 = 2 , is called a proportion. 12 24 Read the proportion 1 = x15675 “1 is to 15 as x is to 675.” CONFIDENTIAL

1 = x 15 675 675 675 Using Ratios The ratio of faculty members to students at a college is 1:15. There are 675 students. How many faculty members are there? Faculty= 1 Students15 Write a ratio comparing faculty to students. 1= x 15675 Write a proportion. Let x be the number of faculty members. Since x is divided by 675, multiply both sides of the equation by 675. x = 45 There are 45 faculty members. CONFIDENTIAL

Now you try! 1) The ratio of games won to games lost for a baseball team is 3 : 2. The team won 18 games. How many games did the team lose? 1) 12 CONFIDENTIAL

A rate is a ratio of two quantities with different units, such as or 34mi , 2gal Rates are usually written as unit rates. A unit rate is a rate with a second quantity of 1 unit, such as 34mi , 2gal or 17 mi/gal. You can convert any rate to a unit rate. CONFIDENTIAL

Finding Unit Rates Garryate 53.5 hot dogs in 12 minutes to win a contest. Find the unit rate. Round your answer to the nearest hundredth. 53.5= x 12 1 Write a proportion to find an equivalent ratio with a second quantity of 1. 4.46 ≈ x Divide on the left side to find x. The unit rate is approximately 4.46 hot dogs per minute. CONFIDENTIAL

Now you try! 1) Cory earns $52.50 in 7 hours. Find the unit rate. 1) 7.5 CONFIDENTIAL

Conversion factor A rate such as 12in. , 1 ft in which the two quantities are equal but use different units, is called a conversion factor. To convert a rate from one set of units to another, multiply by a conversion factor. CONFIDENTIAL

Conversion factor A) The earth’s temperature increases, as you go deeper underground. In some places, it may increase by 25°C per kilometer. What is this rate in degrees per meter? 25°C× 1km 1km1000m To convert the second quantity in a rate, multiply by a conversion factor with that unit in the first quantity. 0.025°C 1m The rate is 0.025°C per meter. CONFIDENTIAL

B) The dwarf sea horse Hippocampus zosterae swims at a rate of 52.68 feet per hour. What is this speed in inches per minute? Step1:Convert the speed to inches per hour. To convert the first quantity in a rate, multiply by a conversion factor with that unit in the second quantity. 52.68ft× 12 in 1h1ft 632.16 in. 1h The speed is 632.16 inches per hour. Next page  CONFIDENTIAL

Step2:Convert this speed to inches per minute. 632.16 in× 1 h 1h60 min To convert the second quantity in a rate, multiply by a conversion factor with that unit in the first quantity. 10.536 in 1 min The speed is 10.536 inches per minute. • Check that the answer is reasonable. • The answer is about 10 in./min. • There are 60 min in 1 h, so 10 in./min is 60 (10) = 600 in./h. • • There are 12 in. in 1 ft, so 600 in./h is • 600= 50 ft/h. This is close to the rate • 12 • given in the problem, 52.68 ft/h. CONFIDENTIAL

Now you try! • A cyclist travels 56 miles in 4 hours. What is the cyclist’s speed in feet per second? Round your answer to the nearest tenth, and show that your answer is reasonable. • 1 mile = 5280 feet 1) 20.53 ft/sec CONFIDENTIAL

Cross Products Property In the proportion a = c, b d the products a · d and b · c are called cross products. You can solve a proportion for a missing value by using the Cross Products Property. CONFIDENTIAL

Solving Proportions Solve each proportion. A) 5 = 3 9 w 5 = 3 9 w 5 (w)=9 (3) Use cross products. 5w = 27 5w = 27 5 5 Divide both sides by 5. w = 27 5 CONFIDENTIAL

B) 8 = 1 x + 10 12 8 = 1 x + 10 12 8 (12)=1 (x + 10) Use cross products. 96 = x + 10 -10-10 Subtract 10 from both sides. 86 = x CONFIDENTIAL

Now you try! Solve each proportion. 1) -5 = y 2 8 1) y = -20 2) g + 3 = 7 5 4 2) g = 5.75 CONFIDENTIAL

A scale is a ratio between two sets of measurements, such as 1 in : 5 mi. A scale drawing or scale model uses a scale to represent an object as smaller or larger than the actual object. A map is an example of a scale drawing. A scale written without units, such as 32 : 1, means that 32 units of any measure correspond to 1 unit of that same measure. CONFIDENTIAL

Scale Drawings and Scale Models A) On the map, the distance from Houston to Beaumont is 0.8 in. What is the actual distance? 1 in : 100 mi Solution: map = 1 in actual 100 mi Write the scale as a fraction. 0.8 in = 1 in x 100 mi Let x be the actual distance. x · 1 = 100 (0.8) Use cross products to solve. x = 80 The actual distance is 80 mi. CONFIDENTIAL

B) The actual distance between Bryan- College Station and Galveston is 127 mi. What is this distance on the map? 1 in : 100 mi Solution: map = 1 in actual 100 mi Write the scale as a fraction. x = 1 in 127 100 mi Let x be the distance on the map. 127 = 100x Use cross products to solve. 127 = 100x 100 100 Since x is multiplied by 100, divide both sides by 100 to undo the multiplication. 1.27 = x The actual distance is 80 mi. CONFIDENTIAL

Now you try! 1) A scale model of a human heart is 16 ft long. The scale is 32:1. How many inches long is the actual heart it represents? 1) 0.5 inch CONFIDENTIAL

4) Lydia wrote 1 pages of her science report in one 2 hour. What was her writing rate in pages per minute? 4 4) 3 pages per minute 40 Assessment 1) The ratio of the sale price of a jacket to the original price is 3 : 4. The original price is $64. What is the sale price? 1) $48 2) 50 times/sec 2) Find the unit rate. A computer’s fan rotates 2000 times in 40 seconds. 3) Find the unit rate. Twelve cows produce 224,988 pounds of milk. 3) 18749 pounds of milk/cow CONFIDENTIAL

Solve each proportion. 5) 3 = 1 z 8 8) f + 3 = 7 12 2 5) z = 24 8) f = 39 6) x = 1 3 5 9) -1 = 3 5 2d 6) x = 0.6 9) d = -7.5 7) b = 3 4 2 10) 3 = s - 2 14 21 7) b = 6 10) s = 6.5 CONFIDENTIAL

Let’s review Rates, Ratios, and Proportions A ratio is a comparison of two quantities by division. The ratio of a to b can be written a:b or a , b where b ≠ 0. Ratios that name the same comparison are said to be equivalent. A statement that two ratios are equivalent, such as 1 = 2 , is called a proportion. 12 24 Read the proportion 1 = x15675 “1 is to 15 as x is to 675.” CONFIDENTIAL

1 = x 15 675 675 675 review Using Ratios The ratio of faculty members to students at a college is 1:15. There are 675 students. How many faculty members are there? Faculty= 1 Students15 Write a ratio comparing faculty to students. 1= x 15675 Write a proportion. Let x be the number of faculty members. Since x is divided by 675, multiply both sides of the equation by 675. x = 45 There are 45 faculty members. CONFIDENTIAL

review A rate is a ratio of two quantities with different units, such as or 34mi , 2gal Rates are usually written as unit rates. A unit rate is a rate with a second quantity of 1 unit, such as 34mi , 2gal or 17 mi/gal. You can convert any rate to a unit rate. CONFIDENTIAL

review Finding Unit Rates Garryate 53.5 hot dogs in 12 minutes to win a contest. Find the unit rate. Round your answer to the nearest hundredth. 53.5= x 12 1 Write a proportion to find an equivalent ratio with a second quantity of 1. 4.46 ≈ x Divide on the left side to find x. The unit rate is approximately 4.46 hot dogs per minute. CONFIDENTIAL

review Conversion factor A rate such as 12in. , 1 ft in which the two quantities are equal but use different units, is called a conversion factor. To convert a rate from one set of units to another, multiply by a conversion factor. CONFIDENTIAL

review Conversion factor A) As you go deeper underground, the earth’s temperature increases. In some places, it may increase by 25°C per kilometer. What is this rate in degrees per meter? 25°C× 1km 1km1000m To convert the second quantity in a rate, multiply by a conversion factor with that unit in the first quantity. 0.025°C 1m The rate is 0.025°C per meter. CONFIDENTIAL

review B) The dwarf sea horse Hippocampus zosterae swims at a rate of 52.68 feet per hour. What is this speed in inches per minute? Step1:Convert the speed to inches per hour. To convert the first quantity in a rate, multiply by a conversion factor with that unit in the second quantity. 52.68ft× 12 in 1h1ft 632.16 in. 1h The speed is 632.16 inches per hour. Next page  CONFIDENTIAL

review Step2:Convert this speed to inches per minute. 632.16 in× 1 h 1h60 min To convert the second quantity in a rate, multiply by a conversion factor with that unit in the first quantity. 10.536 in 1 min The speed is 10.536 inches per minute. • Check that the answer is reasonable. • The answer is about 10 in./min. • There are 60 min in 1 h, so 10 in./min is 60 (10) = 600 in./h. • • There are 12 in. in 1 ft, so 600 in./h is • 600= 50 ft/h. This is close to the rate • 12 • given in the problem, 52.68 ft/h. CONFIDENTIAL

review Cross Products Property In the proportion a = c, b d the products a · d and b · c are called cross products. You can solve a proportion for a missing value by using the Cross Products Property. CONFIDENTIAL

review Solving Proportions Solve each proportion. A) 5 = 3 9 w 5 = 3 9 w 5 (w)=9 (3) Use cross products. 5w = 27 5w = 27 5 5 Divide both sides by 5. w = 27 5 CONFIDENTIAL

review B) 8 = 1 x + 10 12 8 = 1 x + 10 12 8 (12)=1 (x + 10) Use cross products. 96 = x + 10 -10-10 Subtract 10 from both sides. 86 = x CONFIDENTIAL

review A scale is a ratio between two sets of measurements, such as 1 in : 5 mi. A scale drawing or scale model uses a scale to represent an object as smaller or larger than the actual object. A map is an example of a scale drawing. A scale written without units, such as 32 : 1, means that 32 units of any measure correspond to 1 unit of that same measure. CONFIDENTIAL

review Scale Drawings and Scale Models A) On the map, the distance from Houston to Beaumont is 0.8 in. What is the actual distance? 1 in : 100 mi Solution: map = 1 in actual 100 mi Write the scale as a fraction. 0.8 in = 1 in x 100 mi Let x be the actual distance. x · 1 = 100 (0.8) Use cross products to solve. x = 80 The actual distance is 80 mi. CONFIDENTIAL

review B) The actual distance between Bryan- College Station and Galveston is 127 mi. What is this distance on the map? 1 in : 100 mi Solution: map = 1 in actual 100 mi Write the scale as a fraction. x = 1 in 127 100 mi Let x be the distance on the map. 127 = 100x Use cross products to solve. 127 = 100x 100 100 Since x is multiplied by 100, divide both sides by 100 to undo the multiplication. 1.27 = x The actual distance is 80 mi. CONFIDENTIAL

You did a great job today! CONFIDENTIAL

Grade 8 Pre-Algebra Rates, Ratios, and Proportions