Enter your Sign-on user name and password.

Forgot password?
  • Follow us on:
Loading video...

Start Learning Now

Our free lessons will get you started (Flash® 10 required).
Get immediate access to our entire library.

Sign up for Educator.com

Features Overview

  • Get on-demand access to our complete library
  • Search and jump to exactly what you need to learn
  • Track your progress
  • Download practice and lesson files
  • *Ask questions and get answers from our community & instructors

Proportions

  • Ratios that are equal form a proportion.
  • The Cross Products Property is true because of the Multiplication Property of Equality.
  • There are two ways to solve a proportion. You may be able to create an equivalent proportion by finding equivalent ratios by multiplying or dividing the numerator and denominator by the same number. The second way, the preferred method, is to use cross products and then solve for the missing number by using division.

[9/x] = [45/10]

  • 45x = 9 ×10
  • 45x = 90
  • x = 90 ÷45

x = 2

[7/35] = [x/20]

  • 35x = 20 ×7
  • 35x = 140
  • x = 140 ÷35

x = 4

[2/x] = [5/15]

  • 5x = 2 ×15
  • 5x = 30
  • x = 30 ÷5

x = 6

[x/20] = [6/30]

  • 30x = 6 ×20
  • 30x = 120
  • x = 120 ÷30

x = 4

[7/13] = [14/x]

  • 7x = 13 ×14
  • 7x = 182
  • x = 182 ÷7

x = 26

[8/x] = [16/7]

  • 16x = 8 ×7
  • 16x = 56
  • x = 56 ÷16

x = 3[1/2]

You exchange $ 235 for 1501.97 Chinese Yuan. Find the unit rate of exchange to the nearest hundredth.

  • [$ 235/1501.97] = [$ 1/e]
  • 235e = 1501.97
  • e = 1501.97 ÷235

e = 6.39

Does this ratio form a proportion? Explain.
[65/25], [13/5]

  • [(65 ÷5)/(25 ÷5)] = [13/5]

Yes. You can create an equivalent ratio by dividing.

A car can travel 155 miles on 5 gallons of gas. How far can the car travel on 7 gallons of gas?

  • [155/5] = [x/7]
  • 5x = 155 ×7
  • 5x = 1085
  • x = 1085 ÷5

x = 217 miles

You are making a map of the state of Colorado that is to scale. Colorado is approximately 380 miles long and 280 miles wide in real life. If the Colorado on your map is going to be 14 inches wide, how long will it be?

  • [380 mi long/280 mi wide] = [(x in long)/14 in wide]
  • 280x = 380 ×14
  • 280x = 5320
  • x = 5320 ÷280

x = 19 in

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.

Answer

Proportions

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

Mathematics: Pre Algebra