Step by step
The question
Question: 2 and 1/4 liters in 3/4 minute: how much is that per minute?
A unit rate says how much for 1 minute.
Per minute means: divide by the minutes.
1 Write the rate
Liters divided by minutes: 2 and 1/4 ÷ 3/4.
Careful!
Not the other way round.
That would be minutes per liter.
2 Divide
2 and 1/4 is a mixed number.
Each whole one is 4/4.
So we do 2 times 4, plus 1.
The bottom stays 4.
2 times 4 plus 1 is 9.
So it is 9/4.
Dividing by a fraction is the same as times its flip.
Keep the first number.
Change divide to times.
Turn the second fraction upside down.
So 3/4 becomes 4/3, and divide becomes times.
Before we multiply, we make the numbers smaller.
9 on top and 3 at the bottom both divide by 3.
4 on top and 4 at the bottom both divide by 4.
A top and a bottom divided by the same number: the answer stays the same.
So we multiply smaller numbers.
3 times 1 is 3.
So the unit rate is 3 liters per minute.
3 Check
Let's check: 3 liters per minute, for 3/4 minute.
3 times 3/4 is 9/4.
That is the liters we started with.
So the answer is right!
Let's look back.
First: write the rate.
Then: divide.
Last: check.