Step by step
The question
Question: A boat sails 54 km in 3 hours.
What is its speed in km/h?
1 Find what we know
What do we know?
The boat goes 54 km in 3 hours.
What do we want?
The speed, in km per hour.
2 Name the unknown
We don't know the speed.
So we call it x km/h.
Careful!
Speed in km/h means how many km in 1 hour.
How far we go: speed times time.
Let's draw it.
The boat starts here.
It goes x km in each hour, for 3 hours.
The whole trip: 54 km.
3 Write the equation
In words: speed times time makes the distance.
So the equation is 3x = 54.
Now we solve it.
Is x alone now?
Not yet: 3x means 3 times x.
How do we remove it?
4 Remove the 3
To remove times 3, we divide by 3.
We do it on both sides, so they stay equal.
3 divided by 3 is 1.
They cancel each other.
So just x is left.
54 divided by 3 is 18.
So x = 18.
5 Answer the question
So the speed is 18 km/h.
6 Check
Let's check in the story.
18 km/h for 3 hours: 18 times 3 is 54 km, like the story says.
Check it with the picture.
The boat goes 18 km/h: in 3 hours that is 54 km, the whole trip.
So the answer is right!
Let's look back.
First: find what we know.
Then: name the unknown.
Then: write the equation.
Then: solve it.
Then: answer the question.
Last: check.