How to add negative numbers - SAT Math
Card 0 of 3
a, b, c are integers.
abc < 0
ab > 0
bc > 0
Which of the following must be true?
a, b, c are integers.
abc < 0
ab > 0
bc > 0
Which of the following must be true?
Let's reductively consider what this data tells us.
Consider each group (a,b,c) as a group of signs.
From abc < 0, we know that the following are possible:
(–, +, +), (+, –, +), (+, +, –), (–, –, –)
From ab > 0, we know that we must eliminate (–, +, +) and (+, –, +)
From bc > 0, we know that we must eliminate (+, +, –)
Therefore, any of our answers must hold for (–, –, –)
This eliminates immediately a > 0, b > 0
Likewise, it eliminates a – b > 0 because we do not know the relative sizes of a and b. This could therefore be positive or negative.
Finally, ac is a product of negatives and is therefore positive. Hence ac < 0 does not hold.
We are left with a + b < 0, which is true, for two negatives added must be negative.
Let's reductively consider what this data tells us.
Consider each group (a,b,c) as a group of signs.
From abc < 0, we know that the following are possible:
(–, +, +), (+, –, +), (+, +, –), (–, –, –)
From ab > 0, we know that we must eliminate (–, +, +) and (+, –, +)
From bc > 0, we know that we must eliminate (+, +, –)
Therefore, any of our answers must hold for (–, –, –)
This eliminates immediately a > 0, b > 0
Likewise, it eliminates a – b > 0 because we do not know the relative sizes of a and b. This could therefore be positive or negative.
Finally, ac is a product of negatives and is therefore positive. Hence ac < 0 does not hold.
We are left with a + b < 0, which is true, for two negatives added must be negative.
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Add: 
Add:
Anytime a negative number is added, it is similar to subtraction. Recovert the expression to the correct form. Simplify.
The correct answer is 
.
Anytime a negative number is added, it is similar to subtraction. Recovert the expression to the correct form. Simplify.
The correct answer is
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Add the negative numbers: 
Add the negative numbers:
In order to add the negative numbers, we need to eliminate the double signs and the parentheses. A positive and a negative sign will result in a negative sign.
Evaluate the terms on the right.
The answer is: 
In order to add the negative numbers, we need to eliminate the double signs and the parentheses. A positive and a negative sign will result in a negative sign.
Evaluate the terms on the right.
The answer is:
Compare your answer with the correct one above