Step by step
The question
Question: A boat sails 20 km in 2 hours.
What is its speed in km/h?
1 Find what we know
What do we know?
The boat goes 20 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.
3 Write the equation
In words: speed times time makes the distance.
So the equation is 2x = 20.
Now we solve it.
4 Remove the 2
2x means 2 times x.
We want just x.
To remove times 2, we divide by 2.
We do it on both sides, so they stay equal.
2 divided by 2 is 1.
So just x is left.
20 divided by 2 is 10.
So x = 10!
5 Answer the question
So the speed is 10 km/h.
6 Check
Let's check in the story.
10 km/h for 2 hours: 10 times 2 is 20 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.