# combining fractions

• Nov 13th 2006, 01:42 PM
demo
combining fractions
If You know how to Combine Like Fractions or know of a site where I can plug in problems and get tips and how to do them then PLEASE help me!

9) -2(c-d) + (c-d) - 6(c-d)

10) -3(4x + -2y) - 2(x+3y) -2(2x+6y)

These are two problems I need hints on just to randomly pick!
• Nov 13th 2006, 01:50 PM
topsquark
Quote:

Originally Posted by demo
If You know how to Combine Like Fractions or know of a site where I can plug in problems and get tips and how to do them then PLEASE help me!

9) -2(c-d) + (c-d) - 6(c-d)

10) -3(4x + -2y) - 2(x+3y) -2(2x+6y)

These are two problems I need hints on just to randomly pick!

First tip: Type your problems in a black font. It shows up much better on white. Really!

Let's take the first term of the first problem:

-2(c-d) = (-2)(c) + (-2)(-d) = -2c + 2d.

This is called the distributive law and it always works like I did it above.

So:
9) -2(c - d) + (c - d) - 6(c - d)

= (-2)(c) + (-2)(-d) + c - d + (-6)(c) + (-6)(-d)

= -2c + 2d + c - d - 6c + 6d

= -2c + c - 6c + 2d - d + 6d <-- I just rearranged the line above to group terms with c and d.

Now we can reverse the distributive law. Look at the first 3 terms:
-2c + c - 6c = (-2 + 1 - 6)c = -7c

Likewise:
2d - d + 6d = (2 - 1 + 6)d = 7d

Putting it all together:
-2(c - d) + (c - d) - 6(c - d) = -7c + 7d

See if you can do the other one:
-3(4x + -2y) - 2(x+3y) -2(2x+6y)

I got -10x - 12y.

-Dan
• Nov 13th 2006, 01:57 PM
demo
Thanks...I'll try it!
• Nov 13th 2006, 02:19 PM
demo
so the answer for #9 is -7 + 7d ?

and for 4(x + 5y) + 3(x + 6y) + 6(3x + 8y)
I got 25x + 66y
• Nov 13th 2006, 02:48 PM
topsquark
Quote:

Originally Posted by demo
so the answer for #9 is -7 + 7d ?

and for 4(x + 5y) + 3(x + 6y) + 6(3x + 8y)
I got 25x + 66y

The answer for 9 is -7c + 7d.

4(x + 5y) + 3(x + 6y) + 6(3x + 8y)

= 4x + 20y + 3x + 18y + 18x + 48y

= 4x + 3x + 18x + 20y + 18y + 48y

= (4 + 3 + 18)x + (20 + 18 + 48)y

= 25x + 86y

-Dan
• Nov 13th 2006, 03:01 PM
demo
Finally Done!
damnit!
I was so close to..well thanks!