Grade 7 · Unit 1 · Lesson 7 · part 2 of 5
Zoomy the racing snail
In 6th grade you changed one unit at a time: 3 feet is 36 inches, because 1 foot is 12 inches.
Zoomy the racing snail
In 6th grade you changed one unit at a time: 3 feet is 36 inches, because 1 foot is 12 inches. A rate has two units, like miles per hour, so this year you change both. The idea is still the thread:
A proportional relationship always multiplies by the same number, the unit rate.
Change one unit, then change the other. Each change is a multiply or a divide by one number.
Meet Zoomy, a racing garden snail. A garden snail's top speed is about 0.029 miles per hour. How far can Zoomy go in a one-minute race? Miles per hour is no help for a one-minute race measured in feet, so convert the rate to feet per minute, one unit at a time.
Sense check: feet are smaller than miles, so there are more of them. The number should get bigger. 153 is bigger than 0.029. Good.
Sense check: a minute is shorter than an hour, so Zoomy covers less in a minute. The number should get smaller. 2.55 is smaller than 153. Good.
So Zoomy goes about 2 and a half feet in a one-minute race. Not fast, but every step was just multiplying or dividing by one number.