8th grade Ch 3 L3

A color printer can print 36 pages in 3 minutes and 108 pages in 9 minutes. If the number of pages varies directly with the time, at what rate is the color printer printing?

Mathematical Equivalence

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Answer explanation

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CCSS.HSF-LE.A.1B

A new compact car can travel 288 miles on nine gallons of gas. The distance driven in miles y varies directly with the number of gallons of gas x. This situation can be represented by the equation y = 32x.

Graph the equation on the coordinate plane.

Answer explanation

A new compact car can travel 288 miles on nine gallons of gas. The distance driven in miles y varies directly with the number of gallons of gas x. This situation can be represented by the equation y = 32x.

How many miles per gallon does the car get?

Mathematical Equivalence

ON

Answer explanation

A new compact car can travel 288 miles on nine gallons of gas. The distance driven in miles y varies directly with the number of gallons of gas x. This situation can be represented by the equation y = 32x.

The distance y traveled by a hybrid car using x gallons of gas can be represented by y = 42x. Which car gets better gas mileage?

• The hybrid car gets better gas mileage because it travels 42 miles per gallon, compared to 32 miles per gallon for the compact car.

• The compact car gets better gas mileage because it travels 32 miles per gallon, compared to 42 miles per gallon for the hybrid car.

• Both cars get the same gas mileage because they both travel the same distance per gallon.

• Neither car gets good gas mileage because both travel less than 50 miles per gallon.

Answer explanation

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CCSS.8.EE.C.7B

Annie's current earnings are shown in the table. She was offered a new job that will pay $7.25 per hour. Assume that her earnings vary directly with the number of hours worked. Which job pays more an hour?

• Annie's current job pays $6.50 per hour, so the new job pays more per hour.

• Annie's current job pays $7.50 per hour, so her current job pays more per hour.

• Both jobs pay the same amount per hour.

• Annie's current job pays $8.00 per hour, so her current job pays more per hour.

Answer explanation

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CCSS.HSF-LE.A.1B

Dusty’s earnings vary directly with the number of papers he delivers. The relationship is shown in the graph below. Determine the amount that Dusty earns for each paper he delivers.

Mathematical Equivalence

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CCSS.8.EE.B.5

The weight of an object on Mars varies directly with its weight on Earth. An object that weighs 50 pounds on Mars weighs 150 pounds on Earth. If an object weighs 120 pounds on Earth, write and solve a direct variation equation to find how much an object would weigh on Mars.

• 40 pounds (on Mars)

• 60 pounds (on Mars)

• 100 pounds (on Mars)

• 80 pounds (on Mars)

Answer explanation

Determine whether each linear function is a direct variation. If so, state the constant of variation. If not, explain why not.

• Yes, it is a direct variation. The constant of variation is 4.

• No, it is not a direct variation because the ratio y/x is not constant.

• No, it is not a direct variation because the graph does not pass through the origin.

• Yes, it is a direct variation. The constant of variation is 5.

Answer explanation

Determine whether each linear function is a direct variation. If so, state the constant of variation. If not, explain why not.

• Yes, it is a direct variation. The constant of variation is 1.

• No, it is not a direct variation because the ratio y/x is not constant.

• No, it is not a direct variation because the graph does not pass through the origin.

• No, it is not a direct variation because the constant of variation is not defined.

Answer explanation

The number of centimeters varies directly with the number of inches. Find the measure of an object in centimeters if it is 50 inches long.

Mathematical Equivalence

ON

Answer explanation