Proportion
Proportion
Proportion:
A proportion is really two ratios that are equivalent to each other. Here is an example:
There are several ways to tell if two ratios form a proportion.
1st method: Check to see if the same scale factor was used on top and bottom.
2nd method: Try and simplify one or both of the ratios.
In this example, we could reduce the second ratio. Check it out:
Once again, we can see that the two ratios are equivalent. Therefore, they must form a proportion.
3rd method: Cross products: Multiply the numbers that are diagonal to each other. If the products are equal, the two ratios form a proportion.
5 x 28 = 140
7 x 20 = 140
Check out what happens when you do not have a proportion:
2 x 45 = 90
3 x 28 = 84
Here, the cross products are not the same. This shows that the two ratios are not a proportion.
These steps are also useful in finding the missing number in a proportion.
Illustration: Here are some examples of finding the missing number in a proportion using all three methods.
1.) 
Determine if the following are in proportion : 11, 121, 9, 99 | |||
| Right Option : A | |||
| View Explanation | |||
Find the fourth proportion to: 78, 642,13 | |||
| Right Option : D | |||
| View Explanation | |||
If | |||
| Right Option : B | |||
| View Explanation | |||
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