Expert: Scott A Wilson - 11/4/2009

Question
Simplify Expression. How do you know when to add or subtract? Example -5x +16-8x-14+10x = -13x+2+10x = -3x+2. The part I dont get is, how do you know which sign to use

Answer
The sign in front tells you.
-5x means subtract 5x.
+16x means to add 16x; if in front, it would be 16x.
-8x means to subtract 8x.
etc.

To make one more move on the left side, the terms can be rearranged when dealing with + and -.

This gives -13x+10x = -3x, so we have -3x + 2 = ... yeah, and there it is.

Example: 1-2+3-4+5-6+7-8+9 can be put in any order.
It could be written as 1+3+5+7+9 - 2-4-6-8.
1+3=4, 4+5=9, 9+7=16; 16+9=25; 25-2=23; 23-4=19; 19-6=13; 13-8=5.

You could also group them both together first.
As in (1+3+5+7+9) - (2+4+6+8); notice that 2, 4, 6, and 8 are all subtracted, but first they are totaled to see how much will be subtracted.
As before, 1+3+5+7=9=25.  This time, 2+4+6+8=20, so 25-20=5, which is the same as last time.