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Grade 8 - Mathematics
2.14 Proportion - I
Two quantities are proportional if they have a same ratio or rate.
Two ratios set equal
Setting two fractions equal
Solved by cross multiplying
Direct or inverse
Example: a/b = c/d
cross products ad =cd
ad and cb are called the cross products of this proportion.
The cross products of any proportion are equal.
the product of extremes in a proportion = the product of means in the proportion.
Cross products can be used to determine whether two ratios are in proportion.
3/2 = 9/x
cross products: 3x = 18
x = 6
q/25 = 52/100
cross products: q x 100 = 25 x 52
100q = 1300
q = 13
Answer the following questions. Also write at least ten examples of your own.
: a, b, c and d are four numbers if a:b = c:d then a, b, c and d are in ______.
: What are the means in 25:30 = 250:300.
12 and 112
30 and 250
42 and 75
: The product of extremes in a proportion = the product of ____ in the proportion.
: The terms at the last of a proportion are called ______.
: The product of ____ in a proportion = the product of means in the proportion.
: If 3,7,9,x are in proportion then value of x = ____.
: What are the extremes in 1:5 = 5:25.
3 and 15
2 and 23
1 and 25
: The terms at the middle of a proportion are called ______.
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