Step by step
The question
Question: A bridge can hold at most 4000 kg.
Each car weighs 1500 kg.
How many cars can be on it?
1 Find what we know
What do we know?
At most 4000 kg.
1500 kg for each car.
What do we want?
How many cars.
2 Name the unknown
We don't know how many cars.
So we call it x.
At most 4000 kg means 4000 kg or less.
We write ≤ 4000 kg.
3 Write the inequality
In words: what the cars make is at most 4000 kg.
So the inequality is 1500x ≤ 4000.
Now we solve it.
4 Remove the 1500
1500x means 1500 times x.
We want just x.
To remove times 1500, we divide by 1500.
We do it on both sides, so the sign stays true.
1500 divided by 1500 is 1.
So just x is left.
We can make 4000/1500 simpler.
It is the same as 8/3.
So x is less than or equal to 8/3.
5 Show it on a number line
6 Answer the question
That is about 2.67.
Cars come in whole numbers.
The biggest whole number up to 2.67 is 2.
So we round down.
Careful!
2.67 rounds to 3 the usual way.
But 3 cars are 4500 kg.
That is too much.
So we round down.
So at most 2 cars.
7 Check
Let's check in the story.
2 cars: 3000 kg.
That is not more than 4000 kg.
But 3 cars would be 4500 kg: too much.
So 2 is the most.
So the answer is right!
Let's look back.
First: find what we know.
Then: name the unknown.
Then: write the inequality.
Then: solve it.
Then: answer the question.
Last: check.