Step by step
The question
Question: solve 7x − 4 = 24.
Let's find x.
We want x by itself.
First we remove the − 4, so 7x is alone.
Then we remove the times 7.
There are four choices.
First we solve it, the normal way.
Then we pick.
Is x alone now?
Not yet: − 4 is still with x.
How do we remove it?
1 Remove the − 4
To remove − 4, we add 4.
We do it on both sides.
Why both sides?
The = sign means both sides are the same amount.
If we change only one side, they are not the same any more.
− 4 and + 4 cancel each other.
They make zero.
24 + 4 = 28.
Now we have 7x = 28.
So after step 1: we added 4, and now we have 7x = 28.
Is x alone now?
Not yet: 7x means 7 times x.
2 Remove the 7
To remove times 7, we divide by 7.
We do it on both sides, so they stay equal.
7 divided by 7 is 1.
They cancel each other.
So just x is left.
28 divided by 7 is 4.
So x = 4!
3 Check
Let's check: put 4 in place of x.
We get 24, the same as the right side.
So x = 4 is right!
4 Pick the choice
Our answer is x = 4.
That is choice B.
5 Why not the others
A is 20/7.
Wrong: took 4 away: 7x = 20.
C is 28.
Wrong: 7x = 28, but we still had to divide by 7.
D is 196.
Wrong: 28 × 7: multiplied instead of dividing.
Let's look back.
First: remove the − 4.
Then: remove the 7.
Then: check.
Then: pick the choice.
Last: why not the others.