Algebra Demystified 2nd Ed

340 algebra De mystif ieD

The manufacturing plant should produce between 10,000 and 25,000

gross per month to keep its monthly costs between $96,000 and

$150,000.

PRACTICE

1. According to Hooke’s law, the force, F (in pounds), required to stretch a
   certain spring x inches beyond its natural length is F = 4.2x. If 7 ≤ F ≤ 14,
   what is the corresponding range for x?


2. The relationship between the Fahrenheit and Celsius temperature scales
   is given by F = ^95 C + . 32 If 52  F≤  ≤  , 3 what is the corresponding range
   for C?


3. A saleswoman’s salary is a combination of an annual base salary of
   $15,000 plus a 10% commission on sales. What level of sales does she
   need to maintain in order that her annual salary range from $40,000 to
   $60,000?


4. The Smith’s electric bills consist of a base charge of $20 plus 12 cents
   per kilowatt-hour. If the Smiths want to keep their electric bill in the
   $80 to $110 range, what range of kilowatt-hours do they need to
   maintain?


5. A particular collect call costs $2.10 plus 50 cents per minute. (The com-
   pany bills in two-second intervals.) How many minutes would a call
   need to last to keep a charge between $4.50 and $6.00?

✔SOLUTIONS

1. 71442
   74214
   7
   42

42

42

14

42

5

3

≤≤ =

≤≤

≤≤

≤

FFx

x

x

x

and..

.

.

.

..

≤≤^10

3

If the force is to be kept between 7 and 14 pounds, the spring will stretch

between^53 and^103 inches beyond its natural length.

PRACTICE

1. According to Hooke’s law, the force,