Introduction - Basic Mathematics for Water and Wastewater Operators - page 5

gal
ft

3

gal/ft =

3

lb
in. 2

pounds persquare inch (psi) =

The same procedures are applied in the following examples.

3

ft
min

3

ft /min =

sec
min

sec/min =

B asiC o peration 2
We must know how to divide by a fraction. For example,

lb
day
min
day

lb
day

day
min

=×

In the above, notice that the terms in the denominator were inverted before the frac-
tions were multiplied. This is a standard rule that must be followed when dividing
fractions.
Another example is

2 2

mm
mm
m

m
mm

2

= mm ×

2

2

2

B asiC o peration 3
We must know how to cancel or divide terms in the numerator and denominator of a
fraction. After fractions have been rewritten in the vertical form and division by the
fraction has been reexpressed as multiplication, as shown above, then the terms can
be canceled (or divided) out.

Note: For every term that is canceled in the numerator of a fraction, a similar term
must be canceled in the denominator and vice versa , as shown below: