**Quote:**

If 7x - 9 = 10x - 18, what is the value of x

This is probably not the 'correct' way of doing it but it is simple and it works.

You must get all the 'x' values on to the same side of the '=' and all the 'number' values on the other side (it helps if each are a positive number).... so ...

7x - 9 = 10x - 18

My first thought would be that 10x is higher than 7x so I will move the 7x over to the right hand side. to do this the 'sign' changes from a positive to a negative (Yes I know the correct terminology is what you do to one side you do to the other so I will try and explain that way next)

-9 = 10x - 7x - 18

(the positive 7x and changed to a negative 7x on the other side)

So now I need the -18 to move to the left (It will become a positive)

18 - 9 =10x - 7x

9 = 3x

Divide both by three gives 3= x

Okay

The 'other' way

**Quote:**

If 7x - 9 = 10x - 18, what is the value of x

What you do to one side you do to the other.... and we want to be left with x = 'a value'

7x - 9 = 10x - 18

To leave the numbers on the left you have to take 7x from both sides

-9 = 10x - 18 - 7x

To take the - 18 out of both side then you have to minus -18

Therefore -9 - (-18 ) = 10x - 7x

a - (-18 ) is the same as +18

so

-9 +18 = 10x - 7x

9 = 3x (to get to x you have to divide both sides by 3)

9/3 = x

3 = x

If you move the x and values to the other side it would still work out but you would be left with

-3 = -x therefore 3 = x

If you can understand that then well done!

I also recommend the Usborne Illustrated dictionary of Maths....... great examples .... covers all KS3 topics