# Idiot's Guides: Basic Math and Pre-Algebra by Carolyn Wheater

By Carolyn Wheater

Idiot's courses: simple arithmetic and Pre-Algebra is helping readers wake up to hurry and relearn the first recommendations of arithmetic, geometry, and pre-algebra. content material contains simple arithmetic operations (addition, subtraction, multiplication, division); observe difficulties; components and multiples; fractions, decimals, and percents; weights and measures; graphs; facts and chance; and algebra and geometry fundamentals. a convention difficulties part can be integrated to aid make stronger the mathematics recommendations. This e-book is perfect for someone wanting a refresher on the way to go front tests, resembling the GED®, ASVAB, and Praxis®.

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Extra resources for Idiot's Guides: Basic Math and Pre-Algebra

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But you just have to divide by 7 and see what happens. 901 z 7 = 128 with 5 left over, so 7 is not a factor. 11 is the next prime, but 901 z 11 is 81 with 10 left over, so 11 is not a factor. Chapter 4: Factors and Multiples 49 But how will you know when you’ve checked enough prime numbers? One way to tell is by comparing the quotient to the divisor. If the quotient is equal to or smaller than the divisor, you can stop. You’ve checked enough. And if you get to the point where the quotient is less than or equal to the divisor and you haven’t found a factor, your number is prime.

If you have \$1,000 in the bank and withdraw \$100, no one at the bank will blink, but if you have \$100 and try to withdraw \$1,000, there’s likely to be an unpleasant reaction. Withdrawing money from your bank account is a subtraction, and subtraction isn’t commutative. DEFINITION The commutative property is a property of addition or multiplication that says that reversing the order of the two numbers will not change the result. The other useful property of addition is the associative property. This property tells us that when adding three or more numbers, you can group the addends in any combination without changing the outcome.

Then when you’re asked to do -14 – 7, you can just think of -14 + -7 and quickly arrive at -21. 6 – (-3) will become 6 + 3, which is clearly 9. This rule is sometimes referred to as “keep, change, change” because you keep the first number as it is, change to addition, and change the second number to its opposite. 42 Part 1: The World of Numbers To subtract signed numbers: • Leave the first number as is. • Change to addition. • Change the second number to its opposite. • Add, following the rules for addition.