Divisibility Rules and Primes Flashcards
When is an integer divisible by 2?
When it is EVEN
When is an integer divisible by 3?
When the sum of the integer’s digits is divisible by 3
When is an integer divisible by 4?
When the integer is divisible by 2 TWICE or if the LAST TWO digits are divisible by 4
When is an integer divisible by 5?
When the integer ends in 0 or 5
When is an integer divisible by 6?
When the integer is divisible by both 2 and 3
When is an integer divisible by 8?
When it is divisible by 2 THREE TIMES, or if the LAST THREE digits are divisible by 8
When is an integer divisible by 9?
When the sum of the integer’s digits is divisible by 9
When is an integer divisible by 10?
When the integer ends in 0
How do you find out if an integer is divisible by 7 or any other number?
Perform long division
If you add/subtract multiples of N, do you get a multiple of N?
Yes
What is the definition of a prime number?
Any positive integer larger than 1 with exactly two factors: 1 and itself
What are the first 10 primes?
2, 3, 5, 7, 11, 13, 17, 19, 23, 29
When will you likely need to use prime factorization on the test?
When a question states that or assumes that a number is an integer
What is the factor foundation rule?
If a is a factor of b, and b is a factor of c, then a is a factor of c.
What is the least common multiple?
The product of all the primes of both numbers (if the two numbers have no primes in common, then their LCM is the product of the two numbers)
