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Lesson 5: Writing & solving proportions

# Writing proportions example

Some examples of writing two ratios and setting them equal to each other to solve proportion word problems. Created by Sal Khan.

## Want to join the conversation?

#1: \$5.78
#2: 11.2 apples
#3: 6 eggs

I'm only asking because I'm not sure if I fully understand this unless I get the answer right...
• and im pretty sure you wouldnt add 11.2 apples it would be 11.
• Lonnie was paid 115.50 for 14 hours of work. work At this rate,how much will Lonnie earn for working 22 hours? How do I set up the problem.
• (115.5/14)*22= \$181.5
(sorry I just do it a very different way.)
• well again sal makes a easy topic complicated
• This equations make no sense, I have no idea on how to learn them, for example; here i have one;

5 erasers cost \$9.85.
Which equation would help determine the cost of 9 erasers?
Normaly I will divide the price by 5 to determin the cost of one eraser and then multiply by 9 to determin the cost of 9, but here the system gives me this;

5/9=\$9.85/x as a final equation that I should have done it ?
Can someone explain to me how this equation makes sense?
• Same trouble here. I don't understand why the cost is the denominator.
• How did other ppls got so many votes? And even some comments are posted even before I was born =O
• Because some people were born before you...
(1 vote)
• hey good
• yeah, super good teacher
• I wonder why he doesn't solve it
• I got 8.96 for question one, 9 divided by 11.50 gives me 1.277 ( repeated sevens) rounded off gives 1.28, times 7 gave me 8.96. Is this incorrect?
• 9 divided by 11.5 does not = 1.2777...
Sounds like you actually did 11.5/9 which does = 1.2777..., which is ok.
Multiply that by 7 and you get the actual answer of 8.94
Your answer is a little off because you rounded too early. Keep 3-4 of the 7's rather than rounding when you did. 1.27777 * 7 = 8.94439, then round to 8.94