4-2 Writing Equations in Slope-Intercept Form
So, the distance the car has traveled after 10 seconds is 155 ft.
ZOOS In 2006, the attendance at the Columbus Zoo and Aquarium was about 1.6 million. In 2009, the zoo s
a. Write a linear equation to find the attendance (in millions) y after x years. Let x be the number of years since
2000.
s attendance in 2020.
b.
a. The attendance increased from 1.6 million to 2.2 million, so it increased by 2.2 1.6 or 0.6 million. This increase
took 3 years, so the increase per year is 0.6 3 or 0.2. This represents the slope. We want x to represent the year
2000, so we need to find the corresponding y-intercept. Use the coordinate (6, 1.6) for 2006 since x = 6 represents
2006.
The linear equation for attendance is y = 0.2x + 0.4.
b. Substitute 20 for x.
The estimated attendance for 2020 is 4.4 million.
In 1904, a dictionary cost 30 . Since then the cost of a dictionary has risen an average of 6 per year.
Write a linear equation to find the cost C of a dictionary y years after 2004.
If this trend continues, what will the cost of a dictionary be in 2020?
a. Let y be the number of years since 1904. The C-intercept is 30, because that was the cost of a dictionary in the y
= 0 year, 1904. The slope is 6 as it represents the rate of increase in price. Write the equation in slope-intercept form
with y as x and C as y.
The cost of a dictionary after y years can be represented by the linear equation C = 30 + 6y.
b. The year 2020 occurs 116 years after 1904, so solve for C when y = 116.
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