SAT SUBJECT TEST MATH LEVEL 1
TOPICS IN ARITHMETIC
ADDITION, SUBTRACTION, MULTIPLICATION, DIVISION
Even though you should know all the basic facts about the arithmetic of real numbers that are summarized in the next KEY FACT, it is important to remember that you can always use your calculator. Of course, you can evaluate 2 + 3 and 2 – 3 in your head. However, if you would hesitate for even a second when asked to evaluate (–2) + (–3) or –2 – (–3), then use your calculator.
Whenever you enter a negative number into your calculator, be sure to put it in parentheses.
Key Fact A3
For any real numbers a and b:
• If either a or b is 0, then ab = 0.
• If ab = 0, then a = 0 or b = 0.
• If a and b are both positive, ab and are positive.
• If a and b are both negative, ab and are positive.
• If either a or b is positive and the other is negative, ab and are negative.
• If both a and b are positive, a + b is positive.
• If both a and b are negative, a + b is negative.
• If either a or b is positive and the other is negative, a + b has the same sign as the number whose absolute value is greater.
• To evaluate a - b, write it as a + (–b) and use the above rules for addition.
The following KEY FACT is a direct consequence of the third and fourth lines of KEY FACT A3.
Key Fact A4
• The product of several numbers is positive if the number of negative factors is even.
• The product of several numbers is negative if the number of negative factors is odd.