nearest Coldstone Creamery is 500 miles away. If it takes them 10 hours to get
there, what was their average speed?
Answer: The key is to realize that if they drive 500 miles in 10 hours, then
they have 500 miles to divide among 10 hours of driving. (It’s just like having 3
quiches to divide among 5 people.) So rewrite it as:
Now you know why miles per hour is the same thing as miles/hour.
Units
Anything you can count or measure has a unit associated with it. Pounds are
units, miles are units, hours are units, miles/hour are units, even noodles can be
units if, like us, you spend your Saturday nights counting and measuring with
noodles.
For a nerdy laugh, check out Wikipedia’s “List of Humorous Units of Measurement.” But don’t convert miles into wiffles or beard-seconds on the SAT.
—Samantha
Knowing how to work with units is ridiculously helpful both for speed and
understanding in many SAT math problems. The rule for working with units is
that you can multiply and divide them just as you would numbers. For example,
when you multiply (or divide) fractions containing units you can cancel units in
the numerator with units in the denominator:
And you can divide using the Simple Rule: