Bell Work 1/22/13 1) Simplify the following ratios: a)b)c) 2) Solve the following proportions: a)b) 3) A map in a book has a scale of 1 in = 112 miles,
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Bell Work 1/22/13• 1) Simplify the following ratios:• a) b) c)
• 2) Solve the following proportions:• a) b)
• 3) A map in a book has a scale of 1 in = 112 miles, and you measured the state of Indiana to be 1.5 inches wide. How many miles wide is the state of Indiana really?
15
10
ft
yds
10
300
m
cm
7
4
days
weeks
1 3 1
5 10
x x
6 15
3 4x x
Agenda• 1) Bell Work• 2) Agenda/Outcomes• 3) Homework check• 4) Proportion Properties• 5) Geometric Mean• 6) Proportion word problems• ) Begin IP
Outcomes• I will be able to:
• 1) Simplify ratios
• 2) Solve proportions
• 3) Use properties of proportions
• 4) Define and use the geometric mean
Ratio Review
• Ratio – a comparison of two quantities in the same units
• To solve:• 1) Convert to the same units(Multiply)• 2) Simplify(Reduce)• Examples:• a) b)
in
ft
12
3
m
cm
50
1000
Parts of a Proportion
d
c
b
a
Think about each side of this proportion as a ratio.How else could we write these ratios?
*a:b and c:d
Each proportion has two parts, 1) extremes 2) means
*The numbers on the outside of the ratio are the extremesAnd the numbers on the inside are the means
On Your Own• Take a few minutes to solve the following.
Decide whether or not each statement is true or false. We’ll do #1 together.
Cross multiply to verify if the “if”statement and the “then” are equal
More Properties of Proportions
• Additional Properties of Proportions
• 3) If , then
• 4) If , then
a c
b d a b
c d
a c
b d a b c d
b d
Examples
1st: Label everything we know
2nd: Use that to look for other things
3rd: Use the proportion they gave us
25
60100
75
25
7560
xx = 20
the ratio of two figures, is theratio of corresponding parts
Geometric Mean
a x
x b
ba
***x is always the geometric mean
***1) If we are looking for the mean, x will remain in the denominator and numerator. 2) If we are given the mean, thatnumber goes in place of x in the denominator and numerator.
Examples
• 1) Find the geometric mean between 4 and 25
• 2) Twelve is the geometric mean between 8 and what other number
Proportions in real-life
• Proportions are very useful in real life. Companies often create scale models of their products before constructing larger models.
• Example 1:An engineer makes model cars so that his 3-inch model represents an 8-foot-long car. (a) What ratio model : car does he use? (Remember to use the same units!)
• (b) Use the ratio from part (a) to find the height of the model if the car is 5 feet tall.
Examples
• 2. The Titanic was 882 feet and 9 inches long. A model of the ship is 2 feet 6 inches long and 6 inches high. What was the approximate height of the Titanic to the nearest inch?
Examples• 3. An architect is to design a skyscraper
that is 200 feet long, 140 feet wide, and 400 feet tall. She would like to build a model so that the similarity ratio of the model to the building is 1:400. What should the length and width of the model be in inches?
Similar Figures
• Similar Polygons: Two polygons such that their corresponding angles are
______________________ and the lengths of corresponding sides are _____________________________.
The symbol for “is similar to” is _______.
congruent
proportional
~
Statement of Proportionality
• Statement of Proportionality: An (extended) equation that relates all of the equal ratios in a polygon. For instance, if we said ∆XYZ ~ ∆VUW, we would have the following statement of proportionality:
XY YZ XZ
VU UW VW
X
Y Z
V
U W
Scale Factor• Scale Factor - The ratio of the lengths of two corresponding sides of two similar polygons.
Theorem 8.1
• If two polygons are similar, then the ratio of their perimeters is equal to the ratios of their corresponding side lengths.
KL LM MN NK KL
PQ QR RS SP PQ
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