SOLUTION: Hi- I'm confused as to why I am getting the wrong answer to the following problem. I don't understand what I'm doing wrong. Please send email me some help. Thanks Problem:

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Question 9420: Hi-
I'm confused as to why I am getting the wrong answer to the following problem. I don't understand what I'm doing wrong. Please send email me some help. Thanks
Problem:
3/4 - (-7/12) - 7/8
what I did was find the LCD which I think is 24. So I made the problem as follows:
18/24 - (-14/24) - 21/24 = -17/24
The way that I came up with my answer is:
18/24 - (-14/24) = 4/24 - 21/24 = -17/24
The answer in the back of my book says the answer should be 11/24 and I don't understand how. Thanks in advance for your help.
Answer by DWL(56) (Show Source):
You can put this solution on YOUR website!
Your not considering your signs when you do your addtion and subtraction.

When you subtract a negative number it is the same as adding it, so:

watch your signs, it can get tricky when you go to fast. Remember when subtacting a negative number you add it.