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Aurelia is driving from Miami to Orlando at a rate of 65 miles per hour. The distance is 235 miles. To the nearest tenth of an hour, how long will the trip take?

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Kareem wants to ride his bike from St. Louis to Champaign, Illinois. The distance is 180 miles. If he rides at a steady rate of 16 miles per hour, how many hours will the trip take?

11.25 hours

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Javier is driving to Bangor, 240 miles away. If he needs to be in Bangor in 4 hours, at what rate does he need to drive?

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Alejandra is driving to Cincinnati, 450 miles away. If she wants to be there in 6 hours, at what rate does she need to drive?

75 mph

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Aisha took the train from Spokane to Seattle. The distance is 280 miles and the trip took 3.5 hours. What was the speed of the train?

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Philip got a ride with a friend from Denver to Las Vegas, a distance of 750 miles. If the trip took 10 hours, how fast was the friend driving?

75 mph

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Solve a Formula for a Specific Variable

In the following exercises, use the formula d = r t .

Solve for t
when d = 350 and r = 70
in general

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Solve for t
when d = 240 and r = 60
in general

t = 4 t = d r

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Solve for t
when d = 510 and r = 60
in general

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Solve for t
when d = 175 and r = 50
in general

t = 3.5 t = d r

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Solve for r
when d = 204 and t = 3
in general

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Solve for r
when d = 420 and t = 6
in general

r = 70 r = d t

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Solve for r
when d = 160 and t = 2.5
in general

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Solve for r
when d = 180 and t = 4.5
in general

r = 40 r = d t

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In the following exercises, use the formula A = 1 2 b h .

Solve for b
when A = 126 and h = 18
in general

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Solve for h
when A = 176 and b = 22
in general

h = 16 h = 2 A b

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Solve for h
when A = 375 and b = 25
in general

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Solve for b
when A = 65 and h = 13
in general

b = 10 b = 2 A h

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In the following exercises, use the formula I = Prt .

Solve for the principal, P for
I = $ 5,480 , r = 4 % ,
t = 7 years
in general

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Solve for the principal, P for
I = $ 3,950 , r = 6 % ,
t = 5 years
in general

P = $ 13 , 166.67 P = I r t

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Solve for the time, t for
I = $ 2,376 , P = $ 9,000 ,
r = 4.4 %
in general

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Solve for the time, t for
I = $ 624 , P = $ 6,000 ,
r = 5.2 %
in general

t = 2 years t = I Pr

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In the following exercises, solve.

Solve the formula 2 x + 3 y = 12 for y
when x = 3
in general

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Solve the formula 5 x + 2 y = 10 for y
when x = 4
in general

y = −5 y = 10 5 x 2

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Solve the formula 3 x y = 7 for y
when x = −2
in general

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Solve the formula 4 x + y = 5 for y
when x = −3
in general

y = 17 y = 5 4 x

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Solve a + b = 90 for b .

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Solve a + b = 90 for a .

a = 90 b

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Solve 180 = a + b + c for a .

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Solve 180 = a + b + c for c .

c = 180 a b

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Solve the formula 8 x + y = 15 for y.

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Solve the formula 9 x + y = 13 for y.

y = 13 9 x

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Solve the formula −4 x + y = −6 for y.

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Solve the formula −5 x + y = −1 for y.

y = −1 + 5 x

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Solve the formula 4 x + 3 y = 7 for y .

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Solve the formula 3 x + 2 y = 11 for y .

y = 11 3 x 4

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Solve the formula x y = −4 for y .

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Solve the formula x y = −3 for y .

y = 3 + x

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Solve the formula P = 2 L + 2 W for L .

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Solve the formula P = 2 L + 2 W for W .

W = P 2 L 2

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Solve the formula C = π d for d .

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Solve the formula C = π d for π .

π = C d

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Solve the formula V = L W H for L .

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Solve the formula V = L W H for H .

H = V L W

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Everyday math

Converting temperature While on a tour in Greece, Tatyana saw that the temperature was 40 o Celsius. Solve for F in the formula C = 5 9 ( F 32 ) to find the Fahrenheit temperature.

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Converting temperature Yon was visiting the United States and he saw that the temperature in Seattle one day was 50 o Fahrenheit. Solve for C in the formula F = 9 5 C + 32 to find the Celsius temperature.

10°C

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Writing exercises

Solve the equation 2 x + 3 y = 6 for y
when x = −3
in general
Which solution is easier for you, or ? Why?

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Solve the equation 5 x 2 y = 10 for x
when y = 10
in general
Which solution is easier for you, or ? Why?

Answers will vary.

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Self check

After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

This is a table that has three rows and four columns. In the first row, which is a header row, the cells read from left to right: “I can…,” “confidently,” “with some help,” and “no-I don’t get it!” The first column below “I can…” reads “use the distance, rate, and time formula,” and “solve a formula for a specific variable.” The rest of the cells are blank.

What does this checklist tell you about your mastery of this section? What steps will you take to improve?

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Source:  OpenStax, Elementary algebra. OpenStax CNX. Jan 18, 2017 Download for free at http://cnx.org/content/col12116/1.2
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