Step by step
The question
Question: A train travels 240 km in 2 hours.
What is its speed in km/h?
1 Find what we know
What do we know?
The train goes 240 km in 2 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 train starts here.
It goes x km in each hour, for 2 hours.
The whole trip: 240 km.
3 Write the equation
In words: speed times time makes the distance.
So the equation is 2x = 240.
Now we solve it.
Is x alone now?
Not yet: 2x means 2 times x.
How do we remove it?
4 Remove the 2
To remove times 2, we divide by 2.
We do it on both sides, so they stay equal.
2 divided by 2 is 1.
They cancel each other.
So just x is left.
240 divided by 2 is 120.
So x = 120.
5 Answer the question
So the speed is 120 km/h.
6 Check
Let's check in the story.
120 km/h for 2 hours: 120 times 2 is 240 km, like the story says.
Check it with the picture.
The train goes 120 km/h: in 2 hours that is 240 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.