Khan Academy Arithmetic Terms

Terms found in Khan Academy's Arithmetic course.
How do you add/subtract decimal numbers?
Line up the decimals, then add/subtract as normal.
How do you multiply decimal numbers?
Multiply as normal, then count the number of spaces before each decimal in the problem; add to the answer.
Improper fraction
A fraction where the numerator is bigger than the denominator.
How do you divide decimal numbers?
On the left side of the division problem, move the decimal over to the right (counting the number of spaces).

Then, on the right side of the division problem, move the decimal the same number of spaces to the right; add decimal to the answer.
Greatest common divisor (greatest common factor)
The largest integer that divides a set of integers without a remainder.
What are the 3 rules to finding the greatest common divisor?
1) Divisor cannot be larger than the difference of the two numbers.

2) Divisor cannot be larger than the smallest number.

3) Divisor must be a factor of the difference, or else the smallest number (whichever is smaller)
Least common multiple
The smallest multiple that is exactly divisible by every member of a set of numbers.
How do you find the least common multiple (elegant method)?
Find the greatest common divisor of the set of numbers, then multiply both integers with one another; divide your answer by the greatest common divisor to get the least common multiple.
Mixed number
A number that has both a whole number and a fraction.
How do you convert a mixed number into an improper fraction?
Multiply the denominator by the whole number, then add the answer to the numerator. Write resulting number over the denominator in the form of a fraction.
How do you convert an improper fraction to a mixed number?
Divide the numerator by the denominator, and apply answer to the mixed number.
Prime number
A natural number (1,2,3...) divisible by exactly two natural numbers: one and itself.