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Pre-Algebra
Classwork: word problems and line of best-fit
Name_______________________
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1. Suppose that on a particular long-distance phone plan, the relationship between the number of
minutes a call lasts and the cost of the call is linear. A 5-minute call costs $1.25 and a 15-minute
call costs $2.25.
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a. Write an equation for the relationship between the cost and the length of the call.
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b. What are the slope and y-intercept in this equation? What do they represent in the context of
the problem?
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c. How much will a 25-minute call cost?
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d. How long can a customer talk for $5.00?
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2. Suppose that evolutionary biologists are studying an extinct animal called the Irish Elk. They
want to examine the relationship between the length of the skull to the length of the antlers. The
biologists found the following data where:
x=length of skull in cm and y=length of one antler in cm.
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x
y
46
31.3
47.1
34.2
48.1
36.6
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a. Find the equation for the line of best fit for this data.
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49
38.6
50.1
41.4
b. If one antler is 43cm, predict how long is the corresponding skull will be. (within a tenth of a
cm)
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c. If the skull is 55cm, predict how long one antler is.
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3. Graph the following data without using a calculator.
X – age of plant 1
2
3
(weeks)
Y – weight (g)
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5.7
9.1
12.5
a. Find the equation for the line of best fit for this data
b. What is the slope and what does it represent?
c. What is the y-intercept and what does it represent?
4
5
15.9
19.4