Rate problems are basically easy but you have to make sure you keep
the units straight. That's because
rate problems involve a lot of multiplying and dividing.
For example, if a guy travels 500 km in 20 hours, we find out his
speed by dividing 500 km by 20 hours
to get 25 km/hour. Notice that km/hour is
a fraction that we get by dividing km by hours.
Likewise, if we know that his speed is 25 km/hour and he travels for 20
hours we find out how far he travels by
multiplying 25 km/hour by
20 hours to get 500 km. This time we
multiply km/hour by hour to end up with just km since we are
multiplying a fraction and a
Lastly, if we know he travels 500 km and his speed is 25 km/hour, we
get his time by dividing 500 km by 25 km/hour
to get 20 hours. This time we divide km by
km/hour to end up with hours. If this seems a little hazy, you might
want to review dividing a
fraction and a whole number.
Sometimes you have to convert the units to solve the problem. For
example, suppose you are given the rate of
25 km per hour and are asked the rate per
minute. Since an hour is 60 minutes we change hours into minutes:
25 km per hour
= 25 km per 60 minutes
= 5/12 km per minute
Algebra: Rates and Proportions Help
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