Intermediate Algebra (11th edition)

SECTION 7.5 Applications of Rational Expressions 403

Solve each formula for the specified variable. See Examples 2 and 3.

9. for G ( physics) 10. for M ( physics)


10. for a (electricity) 12. for b (electricity)


11. for v (chemistry) 14. for T (chemistry)


12. for r (engineering) 16. for V ( physics)


13. for b (mathematics) 18. for n (mathematics)


14. for r (engineering) 20. for x

21.Concept Check In solving the equation for a, what is the first step?

22.Concept Check To solve the following equation for r, what is the first step?

Solve each problem mentally. Use proportions in Exercises 23 and 24.

23.In a mathematics class, 3 of every 4 students are girls. If there are 28 students in the class,
how many are girls? How many are boys?

24.In a certain southern state, sales tax on a purchase of $1.50 is $0.12. What is the sales tax
on a purchase of $9.00?

25.If Marin can mow her yard in 3 hr, what is her rate (in terms of the proportion of the job
per hour)?

26.A van traveling from Atlanta to Detroit averages 50 mph and takes 14 hr to make the trip.
How far is it from Atlanta to Detroit?

The water content of snow is affected by the temper-
ature, wind speed, and other factors present when
the snow is falling. The average snow-to-liquid ratio
is10 in. of snow to 1in. of liquid precipitation. This
means that if 10 in. of snow fell and was melted, it
would produce1in. of liquid precipitation in a rain
gauge. (Source: http://www.theweatherprediction.com))

27.A dry snow might have a snow-to-liquid ratio of
18 to 1. Using this ratio, how much liquid pre-
cipitation would produce 31.5 in. of snow?

28.A wet, sticky snow good for making a snow man might have a snow-to-liquid ratio of 5 to

1. How many inches of fresh snow would 3.25 in. of liquid precipitation produce using
   this ratio?

Use a proportion to solve each problem. See Examples 4 and 5.

29.On a map of the United States, the distance between Seattle and Durango is 4.125 in. The
two cities are actually 1238 miles apart. On this same map, what would be the distance be-
tween Chicago and El Paso, two cities that are actually 1606 mi apart? Round your answer
to the nearest tenth. (Source:Universal Map Atlas.)

30.On a map of the United States, the distance between Reno and Phoenix is 2.5 in. The two
cities are actually 768 miles apart. On this same map, what would be the distance between
St. Louis and Jacksonville, two cities that are actually 919 mi apart? Round your answer
to the nearest tenth. (Source:Universal Map Atlas.)

rp-rq=p+q

m=aab-b

y=

x+z

a-x

E

e

=

R+r

r

S=

n

2

a= 1 a+/ 2 d

1

2

h 1 b+B 2

a=

V-v

t

I=

nE

R+nr

PV

T

=

pv

t

PV

T

=

pv

t

1

a

=

1

b

+

1

c

1

a

=

1

b

+

1

c

F=

GMm

d^2

F=

GMm

d^2