simple algebra

mark m said:
20x-9=13x-7
20x-9+9=13x-7+9
20x=13x-16
20x+13x=-16????
Good to here.
20x-9+9=13x-7+9
Adding correctly
20x = 13x+2
Now SUBTRACT the 13x instead of just moving it with magic.
 
mark m said:
20x-9=13x-7
20x-9+9=13x-7+9
20x=13x+2
20x-13x=13x+2
=7x+2=9
or
=7x-2=5
it's wrong! i'm so lost... i'm too old for this @12h00am
 
relax mark; it's really easy...

Ok to here:
20x=13x+2
20x-13x=13x+2 : 20x - 13x = 13x - 13x + 2 (BOTH sides of the equation!)
so we now have: 7x = 2
therefore, x = 2/7 ; rule: if ax = b, then x = b/a

Now try this one:
4x - 7 = 21 : what does x equal?

And quit complaining about being too old :lol:
 
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