Step by step
The question
Question: An electrician charges $50 plus $30 an hour.
The bill was $170.
How many hours was the job?
1 Find what we know
What do we know?
$50 is paid one time.
$30 for each hour.
Altogether: $170.
What do we want?
How many hours.
2 Name the unknown
We don't know how many hours.
So we call it x.
3 Write the equation
In words: what the hours cost, plus the start, makes the total.
So the equation is 30x + 50 = 170.
Now we solve it.
We want x by itself.
Two things are stuck to x: times 30 and + 50.
First x was times 30.
Then + 50.
To take them off, we go backwards.
First we remove the + 50.
Then the times 30.
4 Remove the + 50
To remove + 50, we take away 50.
We do it on both sides, so they stay equal.
+ 50 and − 50 make zero.
Cross them out.
170 − 50 = 120.
Now we have 30x = 120.
5 Remove the 30
30x means 30 times x.
We want just x.
To remove times 30, we divide by 30.
We do it on both sides, so they stay equal.
30 divided by 30 is 1.
So just x is left.
120 divided by 30 is 4.
So x = 4.
6 Answer the question
So the answer is 4 hours.
7 Check
Let's check in the story.
4 hours at $30 each: 4 times 30 is $120.
Plus the $50 at the start: $170, like the story says.
Does it make sense?
A whole number of hours.
And the total, $170, is more than the $50 start.
So the answer is right!
8 Type it in
The answer box takes 5 characters.
4 has 1.
It fits.
We type 4.
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.