5m+3n+p, -5p+3n, and 2n-m

Put a 1 in front of the two letters which do 
not have a number in front of them.

5m+3n+1p, -5p+3n, and 2n-1m

2. Put a + sign in front of the two expressions which do 
not have a sign in front of them.

+5m+3n+1p, -5p+3n, and +2n-1m

Color every term, the number and the sign before it, 
if any:

1. red if it contains the letter "m".
2. blue if it contains the letter "n".
3. green if it contains the letter "p".

5m+3n+1p, -5p+3n, and 2n-1m

We combine both red terms:

+5m-1m, which gives +4m 

We combine all three blue terms:

+3n+3n+2n, which gives +8n

We combine both green terms:

+1p-5p, which gives -4p 

We put them together:

+4m+8n-4p.

We can remove the + in front:

4m+8n-4p

And we can get rid of the coloring:

4m+8n-4p

That's it!  I'll bet you can now do such problem as this 
all in one step without coloring or putting + signs or 1's
in front!

Edwin