Pre-Algebra Demystified

i.e., substitute the values of the variables in the formula and simplify using

the order of operations.

EXAMPLE

Find the Fahrenheit temperature corresponding to a Celsius temperature of


 10 o. Use the formula F¼^95 Cþ 32 o.

SOLUTION

F¼

9

5

Cþ 32 o

¼

9

5

ð
 10 Þþ 32

¼ 9 ð
 2 Þþ 32

¼
 18 þ 32

¼ 14

Hence, a Celsius temperature of
 10 ois equivalent to a Fahrenheit tempera-

ture of 14o.

EXAMPLE

Find the interest on a loan whose principal (P) is $3,000 with a rate (R) of 6%

for 3 years (T). Use I¼PRT.

SOLUTION

I¼PRT

¼ð$3,000Þð 0 : 06 Þð 3 Þ

¼$ 540

PRACTICE

1. Find the distance (D) in miles an automobile travels in 3 hours (T) at a
   rate (R) of 40 miles per hour. Use D¼RT.


2. Find the Celsius (C) temperature when the Fahrenheit (F) temperature
   is 77o. Use C¼^59 (F
   32 o).


3. Find the volume (V) in cubic inches of a cube when the length of a side
   (s) is 6 inches. Use V¼s^3.


4. Find the perimeter (P) (distance around the outside) of a rectangle if
   the length (l) is 6 feet and the width (w) is 4 feet. Use P¼2lþ2w.


5. Find the current (I) in amperes when the electromotive force (E) is 12
   volts and the resistance (R) is 3 ohms. Use I¼ER.

134 CHAPTER 7 Expression and Equations