Pre-Algebra Formulas Flashcards
What are all the number sets?
ℕ natural (counting) numbers 1,2,3,4,5,…
W whole numbers (natural and 0) 0,1,2,3,4,5,…
ℤ integers (whole and negatives) −3, − 2, − 1,0,1,2,3
ℚ rational numbers (reals that can be fractions) 1/2,3/4,117/121
ℝ − ℚ irrational numbers (reals that can’t be fractions) π, 2, 3
ℝ real numbers (all of the above, just not imaginary
What is ∈ in set notation?
element of, “belongs to,” or “in”
What is ∪ in set notation?
union
What is ∩ in set notation?
intersection
Why is 0 in the identity number for addition and subtraction?
because
adding 0 to something or subtracting 0 from something
doesn’t change its identity
Why is 1 in the identity number for addition and subtraction?
because
multiplying or dividing something by 1 doesn’t change its
identity
What is 2’s divisibility rule?
last digit is 0, 2, 4, 6, 8
What is 3’s divisibility rule?
sum of the digits is divisible by 3
What is 4’s divisibility rule?
last two digits are divisible by 4
What is 5’s divisibility rule?
last digit is 0, 5
What is 6’s divisibility rule?
divisible by 2 and 3
What is 7’s divisibility rule?
5 x last digit + rest of the number is divisible by 7
What is 8’s divisibility rule?
last three digits are divisible by 8
What is 9’s divisibility rule?
sum of the digits is divisible by 9?
What is 10’s divisibility rule?
last digit is 0
