Cross Products Quiz

Isabella worked 50 hours over the past two weeks, and she gets paid by the hour. During the first week of the two-week span, she worked 30 hours and got paid $285.00. How much did she get paid during the second week of the two-week span?

$190.00

In a photograph, a house is 4 inches wide and 6 inches tall. The photograph is enlarged while keeping proportional dimensions, and the width of the house in the enlarged photograph is 9 inches. What is the height of the house in the enlarged photograph?

13.5 inches

Which is a valid proportion?

3/4 = 21/28

Which equation could you use to solve for x in the proportion 4/5 = 9/x ?

4x =45

A car traveled 63 miles on 3 gallons of gas. What proportion can you set up to determine how many miles, m, the car can travel on 7 gallons of gas?

63/3 = m/7

Javed downloaded from the Internet two files that had a combined size of 696 megabytes. The size of the first file was 290 megabytes, and it took 5 minutes to download. Assuming that the files downloaded at a constant speed, how long did it take for the second file to download?

7 minutes

Joanie believes that you cannot use cross products to solve the proportion 50/3 = 75/x for x. She says that if you multiply both sides of the equation by x, you get 50x/3 = 75. Then, if you multiply both sides of the equation by 3, you get 50x = 75, which is a different equation than you would get if you cross multiplied. What mistake did Joanie make in her reasoning?

She assumed that 50x =75 is the equation that you get if you multiply both sides of the equation 50x/ 3 =75 by 3.

Why can you use cross products to solve the proportion 18/5 = x/100 for x?

because 18 times 100 is equal to 5 times x, which means that x is equal to 360

Why is x = 4 a solution to the proportion 14/x = 56/16?

because if you substitute 4 into the equation for x and cross multiply, you get 224 = 224

Claire correctly solved the proportion x/4 = 36/16 for x by using cross products to get the equation 16x =144 and then dividing both sides by 16 to get x=9. She showed that she can use cross products to solve the proportion because she gets the same answer if the solves it as shown. What property allowed her to go from x/4 = 36/16 to x/4 *4 = 36/16 *4?

multiplication property of equality