Number Properties Flashcards
Is 0 odd or even?
Is 0 positive or negative?
0 is even.
0 is neither positive or negative. Problems often use the phrase “positive integers”– read carefully and realize they are talking about 1, 2, 3…. etc
What are the first 10 prime numbers?
2, 3, 5, 7, 11, 13, 17, 19, 23, 29
Data Sufficiency:
Is x prime?
(1) x > 2
(2) x is even
Answer is C– Together they are sufficient.
The only even prime is 2. So if x >2 and x is even, the answer to the question is “NO”. Alone each statement is insufficient.
Do the following have the same meaning? Or are any of them different?
a. 3 is a factor of 12
b. 3 is a divisor of 12
c. 12 is a multiple of 3
d. 12 is divisible by 3
e. 12/3 is an integer
f. 12 is equal to 3n, where n is an integer
g. 12/3 yields a remainder of 0
h. 12 items can be shared among 3 people so that each person has the same number of items
Yes, they all have the same meaning!
The GMAT often writes questions in different ways to confuse you.
It’s important to be able to translate the language into something you understand.
What is the Least Common Multiple of 18 and 24?
We factor each number and then find the “unique factors” – we find the highest power of each different prime factor and then multiply them.
18 = 3<strong>2</strong> * 2
24 = 2<strong>2</strong> * 3
The Least Common Multiple is 32 * 22 = 72
We can confirm this by writing out the multiples:
18: 18, 36, 54, 72
24: 24, 48, 72
Data Sufficiency:
1) If the units digit of N is 0, what do we know about the factors of N?
1) The factors include 2 and 5, because N must be a multiple of 10.
(For any number we want to factor that ends in one or more 0’s, it is easiest to factor the 10’s out first)
What is the prime factorization of 360?
(Draw a factor tree and then write the exponents)
Example:
If the integer N ends with “5000”, what do we know about the factors of N?
From the 3 zeros at the end, the factors include 3 pairs of 2’s and 5’s, because N is a multiple of 1000.
Once we factor out 1000, we know that there is another 5 as a factor, since N/1000 would end with a 5.
Factors include 23 * 54