Ms. Ryan
MCATC
Medical Math
2015-2016





A ratio is composed of 2 related numbers
separated by a colon.
A statement of how two numbers compare.
A comparison of the size of one number to the
size of another number.
Expressed as "a to b" or a : b
Example: 1000 mL : 1 L








Used to compare two ratios or make equivalent
fractions.
A comparison between two values.
Shows the relationship between 2 equal ratios.
It consists of 2 ratios separated by an = sign which
indicates the 2 ratios are equal.
Example: 1000 mg :1 g = 2000 mg : 2 g
The units of measurement in the 2 ratios of a
proportion must be expressed in the same
sequence.
Correct Example: 1000 mg : 1 g = 2000 mg : 2 g
Incorrect Example: 1000 mg : 1 g = 2 g : 2000 m



The means-extremes property of proportions
allows you to cross multiply or set up an
equation , taking the product of the means and
setting them equal to the product of the
extremes.
The numbers on the ends of a proportion are
called the extremes Example: 1000 mg : 1 g =
2000 mg : 2 g
The numbers in the middle are called the means.
Example: 1000 mg : 1 g = 2000 mg : 2 g






To make a proportion a true statement the
product of the means must equal the product
of the extremes.
Known quantities and unknown quantiles
Example: 1500 mg = x g
Known quantity is 1000 mg = 1 g
Unknown quantity is 1500 mg = x g
Then you have 1000 mg : 1 g = 1500 mg : x g


1000 mg : 1 g = 1500 mg : x g
Multiply the extremes


Multiply the means


1 X 1500 = 1500
Set up the equation


1000 X x = 1000 x
1000 x = 1500
Solve for x by dividing both sides by 1000
1000 x = 1500
1000
1000
 x = 1.5 g



Now you have a true statement
1000 mg : 1 g = 1500 mg : 1.5 g
1.
2.
2.
Multiply the unit to by changed by 1000
2 L = _______ ml
2 x 1000 = 2000
2 L = 2000 ml
Move the decimal point of the unit to be changed 3 places
to the right
2.0 would become 2000.0 or 2000 ml
Ratio & proportion
1 L = 1000 ml : 2 L = x ml
multiply the means (the inner) 1000 x 2 = 2000
multiply the extremes (the outer) 1 X x ml = x ml
2000 = x ml
1.
2.
3.
Divide the unit to by changed by 1000
250 mg = _______ g
250 ÷ 1000 = 0.25
250 mg = 0.25 g
Move the decimal point of the unit to be changed 3 places to the
left
250 mg would become 0.25 g
Ratio & proportion
1 g = 1000 mg : x g = 250 mg
multiply the means (the inner) 1000 X x g = 1000 x
multiply the extremes (the outer) 1 X 250 = 250
1000 x = 250
1000
1000
x = 0.25 g







Example: 4 kg = _____ lbs
Known quantity 1 kg = 2.2 lbs
Unknown quantity x lbs = 4 kg
1 kg : 2.2 lbs = 4 kg : x lbs
2.2 x 4 = 8.8
1Xx=x
X = 8.8 lbs




16 oz : 1 pt = 64 oz : x pt
16 oz : 1 pt = 64 oz : x pt-multiply the extremes
16x
16 oz : 1 pt = 64 oz : x pt –multiply the means
and you get 64
Set up to solve for x- 16x = 64