I need help with a certain algebra problem, I have the answers and can't get a certain part of the answer?

Question

I have an algebra problem (basic) and don't remember how to do it.

7x+21y-10x-2y

the answer is supposed to be: 4-3x+19y
the answer I get is: -3x+19y

I just add the two xs and two ys as follows:
7x-10x=-3x
21y-2y=19y
which equals -3x+19y

Basic question is where is the four coming from and how to do this type of problem and know when to do this in a problem. Thank you.

Answer 1

Your answer is correct. Perhaps you are looking in the back of the book for your answer and it happens to be question 4. It would then look as if you are subtracting the 3x from the 4. It is either this, or the answer you have is just incorrect and should be -3x+19y as you thought.

Answer 2

Your answer is correct. In the original expression there are no numbers, just monomials (numbers AND variables multiplies together). You only can combine like terms, and since there were no sole numbers to begin with, a 4 should definitely not be there!





Unless,you copied the problem wrong. ;) Otherwise, looks good!

Answer 3

Your answer is right. unless you think you wrote it wrong..........

my sister does that stuff in highschool