Factorization Flashcards
1
Q
How many factors has the number X?
A
- Find it’s prime factorisation
- All of its factors will be in the form 2^a x 3^b x 5^c
- a+1 choices for the first; b+1 choices for the second; c+1 choices for the last
- The total number of factors is:
a+1 x b+1 x c+1
2
Q
Greatest Common Factor GCF
A
Biggest factor/ divisor shared by two numbers.
- Find prime factorisation of both numbers
- Multiply all the primes that appear in BOTH numbers.
- If two numbers share no primes the GCF is 1
3
Q
Least Common Multiple LCM
A
The smallest number that has both relevant numbers in its divisors.
- Find the prime factorisation of both numbers.
- Find what prime factors appear in both.
- Multiply one of each of the shared primes (don’t count shared primes twice!) with the unshared primes
4
Q
When is a number divisible by 3 ?
A
Sum of digits divisible by 3
5
Q
When is a number divisible by 4?
A
The last two digits of number are divisible by 4
6
Q
When is a number divisible by 5?
A
The last digit is either a 5 or 0
7
Q
When is a number divisible by 6?
A
Even number and sum of digits is divisible by 3
8
Q
When is a number divisible by 8?
A
If the last three digits are divisible by 8
9
Q
When is a number divisible by 9?
A
Sum of digits is divisible by 9
10
Q
Reform: 1/x + 1/y
A
(x+y)/xy
11
Q
GCD LCM FORMULA
A
GCD(x and y) * LCM(x and y) = xy
