catalyst thursday, october 6, 2011 of the 75 teachers at a school, 15 teach mathematics. what...
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CatalystThursday, October 6, 2011
Of the 75 teachers at a school, 15 teach mathematics. What percent of the teachers at the school teach mathematics?
A. 2% B. 5%C. 15% D. 20%
RATIOS and PROPORTIONS REVIEW
By: Teachers who care!
RATIOS & PROPORTIONS A ratio is a comparison of two
numbers by division. To write ratios, use the word to, a
colon, or a fraction bar.EXAMPLE #1: John read 3 books in 4
days. Write the ratio of books to days.
Words: 3 to 4
Colon: 3:4
Fraction: 3/4
RATIOS & PROPORTIONS A proportion is a statement that
two ratios are equal.
EXAMPLE#2: Is a proportion?15
6
5
2
Find the cross products.
65152 30 = 30 TRUEIf TRUE, the
statement is a proportion.
RATIOS & PROPORTIONS
EXAMPLE#3: Is a proportion?
5
3
7
4
Find the cross products.
3754 20 = 21 FALSEIf FALSE, the
statement is NOT a proportion.
RATIOS & PROPORTIONS
EXAMPLE#4: Solve the proportion:10
4
5
Find the cross products.
4510 x2010 x
10 10
2x
Divide both sides by 10.
RATIOS & PROPORTIONS
There are 5 boys and 6 girls in Grant School.
1. What is the ratio of girls to boys using a fraction? 5
6
2. What is the ratio of girls to children in Grant School (use a colon)? 6:11
3. What is the ratio of boys to children in Grant School (use words)?
5 to 11
RATIOS & PROPORTIONS
Are the following proportions?
7
3
9
4
20
9
9
4
27
12
9
4
18
8
9
4
3974 2728
FALSE – Not a proportion
99204 8180
FALSE – Not a proportion
129274 108108
TRUE – this is a proportion
89184 7272
TRUE – this is a proportion
RATIOS & PROPORTIONS
Find the missing numbers to make the following proportions.
21
93
9213 x
x963
x79 9
10
5
4
5410 x2010 x
10 10 2x
9
12
3
4
1
941 x36x
SCALE DRAWINGS A scale drawing is a drawing of an
object with dimensions proportional to those of the actual object. To find lengths from scale drawings, set up and solve proportions.
SCALE DRAWINGS USING PROPORTIONSEXAMPLE#1: ¼ in = 5 ft is a scale
for a rock band’s concert stage.
A. The scale length of the drum stand is 1 in. What is the actual length of the drum stand?
)(
)(
)(
)(
actualobject
drawingobject
ftactual
indrawing
x
1
5
25.
Cross multiply.
1525. x525. x
.25 .2520x
Divide by .25
SCALE DRAWINGS USING PROPORTIONSEXAMPLE#2: ¼ in = 5 ft is a scale
for a rock band’s concert stage.
B. The actual length of the stage is 60 ft. What is the scale length of the stage?
)(
)(
)(
)(
actualobject
drawingobject
ftactual
indrawing
605
25. x
Cross multiply.
x 56025.x515
5 5x3
Divide by 5
SCALE DRAWINGS USING PROPORTIONSGiven a scale of ½ in = 4 ft, find the actual
length for each scale length given.
x
75.2
4
5.
75.245. x115. x
.5 .5
ftx 22
in4
32 in5
x
5
4
5.
545. x205. x
.5 .5
ftx 40
Your Turn to Show What You Know
Yes, you will use the calculator; to show your work, you will set the problem up to show me you know what to do
Pages 142-143, 194-195, and 264-265* Only answer the multiple choice
questions!!!