The equation in choice A is best because the rate of evaporation,
, is the slope. Six feet is the same as 72 inches,
so the beginning water level of the pool, 72, is the y-intercept. x represents the number of days since summer began,
4-2 Writing Equations in Slope-Intercept Form
y represents the total depth of water in the pool in inches.
A manufacturer implemented a program to reduce waste. In 1998 they sent 946 tons of
CCSS SENSE-
waste to landfills. Each year after that, they reduced their waste by an average 28.4 tons.
How many tons were sent to the landfill in 2010?
In what year will it become impossible for this trend to continue? Explain.
a. Write an equation in slope-intercept form: y = 28.4x + 946. Solve for y where x represents the number of years
since 1998 when the program was implemented.
So, 605.2 tons were sent to the landfill in 2010.
b. When the waste sent (y) is 0, a continued trend of reducing waste would be impossible, because a negative
amount of waste is impossible. Solve for x when y = 0.
It would take over 33 years for the waste to equal 0 tons, so then it would become impossible for the trend to
continue in 2032.
COMBINING FUNCTIONS The parents of a college student open an account for her with a deposit of $5000,
and they set up automatic deposits of $100 to the account every week.
a. Write a function d(t) to express the amount of money in the account t weeks after the initial deposit. d(t) = 5000 +
100t
b. The student plans on spending $600 the first week and $250 in each of the following weeks for room and board
and other expenses. Write a function w(t) to express the amount of money taken out of the account each week.
c. Find B(t) = d(t)
w(t). What does this new function represent?
d. Will the student run out of money? If so, when?
a. Let d = the amount of money in the account and t = the number of weeks after the initial deposit. The y-intercept
is the initial deposit of $5000. The slope is 100 as it represents the fixed rate of increase in the account. Write the
equation in slope-intercept form.
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