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A rate is a ratio that expresses some quantity per unit
time.
Examples:
25 mph, 24 feet per second, 36 donuts per hour, etc.
Algebraically
we write Q = R * t
Q is the quantity, R is the rate and t is the time. Given
any two of these parameters, we can solve for the other.
For example:
given the quantity and the rate, find the time;
divide both sides of the equation by R we get
Q / R = t, and rearranging
t = Q / R
For example:
given the quantity Q and the time t, find R;
divide both sides of the equation by t and we get
Q / t = R, and rearranging
R = Q / t
25 mph
is 25 miles per hour Q = 25 miles, t = 1
hour
R =
25 miles / 1 hour
so,
moving at this rate for 2 hours, we've traveled
( 25
miles / 1 hour ) * ( 2 hours ) = 50 miles
Example:
Sarah can run 100 yards in 2 minutes. How far can she run in 3 minutes?
This is a rate problem, Sarah's rate is 100/2 =
50 yards per minute.
= 150 yards (note how minutes cancel)
this
problem can also be done using a proportion:
we have
3 * 50 = 150 yards = x (multiplying both sides by 3)
Download
our free math lesson plan template...and print!!
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