Introduction - Mathematics and Statistics for the Environment - page 22

Cinder block volume is 0.48 ft 3 , which weighs 70 lb; thus,

70 lb
0.48 ft

3

= 145.8 lb/ftdensity of cinde rrblock

3

3
3

Densityofcinderblock
Den

= 1
62 .

45.8 lb/ft
lb/ft

Specificgravity = 2.34

sity of water

1.4.3 t emperature C onversions
Two commonly used methods used to make temperature conversions. We have already demon-
strated the following methods:

• °C = 5/9(°F - 32)
• °F = 9/5(°C) + 32

■ EXAMPLE 1.25
Problem : At a temperature of 4°C, water is at its greatest density. What is that temperature in
degrees Fahrenheit?

Solution:

9/5(°C) + 32 = 9/5(4) + 32 = 7.2 + 32 = 39.2°F

The difficulty arises when one tries to recall these formulas from memory. Probably the easiest
way to recall these important formulas is to remember these basic steps for both Fahrenheit and
Celsius conversions:

1. Add 40°.

2. Multiply by the appropriate fraction (5/9 or 9/5).

3. Subtract 40°.

Obviously, the only variable in this method is the choice of 5/9 or 9/5 in the multiplication step. To
make the proper choice, you must be familiar with the two scales. The freezing point of water is
32° on the Fahrenheit scale and 0° on the Celsius scale. The boiling point of water is 212° on the
Fahrenheit scale and 100° on the Celsius scale.

Note: At the same temperature, higher numbers are associated with the Fahrenheit scale and lower
numbers with the Celsius scale. This important relationship helps you decide whether to
multiply by 5/9 or 9/5.

Now look at a few conversion problems to see how the three-step process works.

■ EXAMPLE 1.26
Problem: Suppose that we wish to convert 240°F to Celsius.

Solution: Using the three-step process, we proceed as follows:

1. Add 40°

240° + 40° = 280°