Lesson 42
Proportions!
My GOAL is to set up and solve proportions to find missing values in real world problems.
Every proportion can be written as an equation!!
A proportion ____________________________________________________
How do we know if they are equivalent / proportional?
_________________________________!
Remember cross-­‐products when we did equivalent fractions and ratios? If two ratios are equal, their cross product must be equal! Sooo… you can make an equation to solve for a missing part! WE TRY: 1.) What equation can be represented by this proportion? 32
96
= 168
56
2.) What equation can be represented by this proportion? 8 .4
28
= 100
30
Now use that knowledge to solve for a missing number! x
12
3.) = 16
48
4.) 5
47.5
= 2
x
Lesson 42
Try These~>
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4. The skull of a crocodile is proportional to its body length. In one species, a 6 foot crocodile has a 2-­‐foot skull. Estimate the length of a crocodile of that species that has a 3.5-­‐foot skull. 5. Suppose you got 13 out of 15 correct on a quiz. Write a proportion and find the percent. Round to the nearest percent. Lesson 42
Math HW
Proportions
Name: _____________________________
Math
HW #42
Date: ______________________________
Period: ___________________
Cross multiply to solve the proportion.
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5.) y = 144
42.3 56.4
6.) 126 = 14
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7.) 30 = 16
x
40
Cross multiply to solve the proportion. Round to the tenths place if necessary.
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Lesson 42
14.) Of the 18 teachers at Lincoln Elementary, 13 are women. Suppose this same ratio
holds for all 68 teachers in the district. Which proportion can be used to find the
total number of women teachers (n)?
Which proportion can be used to solve the problem?
(a) 𝑛
68
5
= 13
(b) 𝑛
68
18
= 13
(c) 𝑛
68
13
= 18
15.) Write the algebraic equation that could be used to solve each proportion. Then solve the equation.
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Rounding Practice: A. Round to the nearest whole number. 1.) 40.957 2.) 153.4999 3.) 0.1523 2.) 432.85 3.) 0.9999 2.) 101.01010 3.) 503.98765 B. Round to the nearest tenth. 1.) 14.6743 C. Round to the nearest hundredth. 1.) 42.7964