Step by step
The question
Question: A car drives 150 km in 3 hours.
What is its speed in km/h?
1 Find what we know
What do we know?
The car goes 150 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.
3 Write the equation
In words: speed times time makes the distance.
So the equation is 3x = 150.
Now we solve it.
4 Remove the 3
3x means 3 times x.
We want just x.
To remove times 3, we divide by 3.
We do it on both sides, so they stay equal.
3 divided by 3 is 1.
So just x is left.
150 divided by 3 is 50.
So x = 50!
5 Answer the question
So the speed is 50 km/h.
6 Check
Let's check in the story.
50 km/h for 3 hours: 50 times 3 is 150 km, like the story says.
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.