BASIC GEOMETRY
7.1: RATIO & PROPORTION
Ratio


Compares two numbers by division.
Writing ratios
a
to b
 a:b

a
b
Slope = ratio of rise/run

Write a ratio expressing the slope of l.
Extended Ratios


Compares more than 2 numbers.
Example: For the rectangle, the ratio of the side
lengths may be written as 3:7:3:7
Extended Ratio Example

The ratio of the side lengths of a triangle is 4:7:5,
and its perimeter is 96 cm. What is the length of
the shortest side?
Proportion

Equation stating that two ratios are equal.
a c

or a:b = c:d

Solving Proportions

b
d
 a&d are the extremes
 b&c are the means
 Use
the cross products property (means = extremes)
a c


→ ad = bc
b d
 Hints: When multiplying sums or differences, use
parenthesis.
Solve each proportion.
A) 7 56

x 72
20
B) x  4

5
x4
Equivalent Forms of Cross Products
Using Properties of Proportions
Given that 18c = 24d, find the ratio of d to c in
simplest form.
Example
Marta is making a scale drawing of her bedroom.
Her rectangular room is 12½ feet wide and 15
feet long. On the scale drawing, the width of her
room is 5 inches. What is the length?
Assignment 1

Page 457 #’s 3-10,14-16,(56)