This is a simple beginner lesson (for about 6th grade level) concerning UNIT RATES.
A unit rate is a ratio where the second term of the ratio is ONE of something. I give examples of unit rates, such as $8.45 per kilogram, 56 miles per hour, 18 pupils to 1 teacher, or 4 balloons for each kid.
Next, we change various non-unit rates to unit rates, which is very simple: all you need to do is DIVIDE. For example, the rate "122 words in 5 minutes" is converted into an unit rate by dividing 122/5, which is 24.4, and writing the "words per minute" after it. So "122 words in 5 minutes" is equivalent to the unit rate 24.4 word per minute.
In the 2nd part of this lesson we solve several word problems involving unit rates.
Word problems involving unit rates — video lesson
Math Mammoth Grade 6 curriculum