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# Introduction to proportional relationships

Proportional relationships are relationships between two variables where their ratios are equivalent. Another way to think about them is that, in a proportional relationship, one variable is always a constant value times the other. That constant is known as the "constant of proportionality".

## Want to join the conversation?

• Why is math so annoying
• for real
• i need more help with this, i don't understand
• Well, a proportional relationship means that the ratio between two variables stayed the same.
Eg.
4 eggs = 2 cups of milk
8 eggs = 4 cups of milk
30 eggs = 15 cups of milk
As you can see, this is a proportional relationship because the ratio between the number of egg and cup of milk is 2:1 through out the table.

A non-proportional relationship os when the two variables have different ratio
Eg.
4 eggs = 4 cups of milk
5 eggs = 6 cups of milk
13 eggs = 12 cups of milk
This is not a proportional relationship because there is no same ratio in the table.
Hope that help.
• why are the things that you are teaching us easier than the questions that khan academy is asking us?
• Actually, some of these problems, you may find in the Khan Academy curriculum. Sal just explains the question expertly.
• what do you need help with? (pls upvote)
• it's not that annoying, it's pretty cool!
• i need help
• with?
• when did he start using that mouse? I like it
• At , what if the cost of cake for 40 servings is \$50. Even if the pattern is not x2, we can see it as another way. We can see it as +10, or +20. Wouldn't that still count?
• There could be a relationship between number of servings and cost, but it wouldn't be proportional because the price per serving is not constant.

\$20 for 10 servings ⇒ \$2/serving
\$30 for 20 servings ⇒ \$1.50/serving
\$50 for 40 servings ⇒ \$1.25/serving
• maths would be so much harder without this