ISEE Upper Level Math : Numbers and Operations
Study concepts, example questions & explanations for ISEE Upper Level Math
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Example Questions
Example Question #3 : Prime Numbers
Which of these numbers is prime?
A prime number has exactly two factors, 1 and itself. We can eliminate four choices by finding other factors:
53 has only 1 and 53 as factors, so it is the only prime among the choices.
Example Question #4 : Prime Numbers
How many composite numbers are between 61 and 80 inclusive?
There are twenty integers from 61 to 80 inclusive. Counting composite numbers can be made easier by weeding out the primes - 61, 67, 71, 73, 79. Removal of these five primes leave fifteen composite numbers.
Example Question #5 : How To Find Out If A Number Is Prime
Which of the following numbers is prime?
The correct answer is 
First, find the approximate square root of the number:
We know this because:
Therefore, we only need to consider prime numbers through
Is 
We know this because:
Therefore, we need to consider the followig prime numbers:
Is 
Example Question #5 : Prime Numbers
How many composite numbers are between and
inclusive?
There are twenty integers from to
inclusive. Counting composite numbers can be made easier by weeding out the primes -
. Removal of these five primes leaves
Example Question #7 : Prime Numbers
Which of the following numbers is prime?
The correct answer to this question is 
Next, determine if the number is divisible by any prime numbers up to and including the square root. In this instance consider the numbers:
Example Question #5 : How To Find Out If A Number Is Prime
How many composite numbers are between 
There are thirty integers from 
Example Question #6 : Prime Numbers
Reduce the fraction:
First, given that 13 times 4 is 52, the numerator can be simplified by taking the square root of 4 and multiplying it by the square root of 13.
Example Question #7 : How To Find Out If A Number Is Prime
How many prime numbers are there between 1 and 20?
2
8
11
7
9
8
A prime number is one in which only itself and 1 can go into it. Therefore, 2, 3, 5, 7, 11, 13, 17, and 19 are the only prime numbers in that set.
Example Question #31 : Factors / Multiples
Which of the following is a prime number?
Which of the following is a prime number?
The answer here is 13, because 13 has no factors other than 1 and itself.
51 is divisible by 3 and 17.
39 is divisible by 13 and 3.
81 is divisible by 9, 3, and 27
Example Question #32 : Factors / Multiples
Find the sum of all the prime numbers between 
The prime numbers between 
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