ISEE Upper Level Quantitative : Numbers and Operations

Study concepts, example questions & explanations for ISEE Upper Level Quantitative

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Example Questions

Example Question #33 : How To Find Out If A Number Is Prime

 and  are prime numbers. 

Which is the greater quantity?

(A) 

(B) 175

Possible Answers:

(B) is greater

It is impossible to determine which is greater from the information given

(A) and (B) are equal

(A) is greater

Correct answer:

(A) is greater

Explanation:

97 is the only prime number between 90 and 100, so . The only two primes between 80 and 90 are 83 and 89, so  or . Therefore, either of the following holds:

or 

(A) must be the greater quantity regardless.

Example Question #35 : How To Find Out If A Number Is Prime

 and  are prime numbers. 

Which is the greater quantity?

(A) 

(B) 80

Possible Answers:

(B) is greater

(A) and (B) are equal

(A) is greater

It is impossible to determine which is greater from the information given

Correct answer:

It is impossible to determine which is greater from the information given

Explanation:

We show that it cannot be determined whether  is greater than, less than, or equal to 80 by choosing two pairs of primes within the given ranges and adding.

Case 1:

.

Case 2:

In each case, , with  and  prime.

Example Question #91 : Factors / Multiples

, and  and  are positive integers.

 is a prime number;  is not a prime number.

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(b) is the greater quantity 

(a) is the greater quantity 

(a) and (b) are equal

It cannot be determined which of (a) and (b) is greater

Correct answer:

It cannot be determined which of (a) and (b) is greater

Explanation:

, and  and  are positive integers, so each of  and  is an integer from 1 to 11 inclusive.

 is a prime number, meaning that it can be equal to 2, 3, 5, 7, or 11. Testing each case:

, which is not prime.

 

, which is not prime.

 

, which is prime - we throw this case out.

 

, which is prime - we throw this case out.

 

, which is not prime.

In the first two cases, ; in the last case, . It cannot be determined which is the greater. 

Example Question #42 : How To Find Out If A Number Is Prime

 and  are positive integers.

 is a prime number.  is not.

Which is the greater quantity?

(a) 5

(b) 

Possible Answers:

(a) and (b) are equal

It cannot be determined which of (a) and (b) is greater

(a) is the greater quantity 

(b) is the greater quantity 

Correct answer:

(b) is the greater quantity 

Explanation:

, and  and  are positive integers.

Therefore,  must be an integer from 1 to 9, as must .

Since  is prime, it can be any of 2, 3, 5, or 7.

Therefore, one of the following must hold:

 

 

 



 

Only in the first case is  not a prime number (8 has four factors - 1, 2, 4, 8), so  and .

Example Question #1 : Least Common Multiple

What is the least common multiple of 15 and 25?

Possible Answers:

Correct answer:

Explanation:

 is the lowest number that is a multiple of both 15 and 25, so we see which is the first number that appears in both lists of multiples.

The multiples of 15:

The multiples of 25:

Example Question #1 : Least Common Multiple

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(a) is greater.

(a) and (b) are equal.

Not enough information is given to answer the question.

(b) is greater.

Correct answer:

Not enough information is given to answer the question.

Explanation:

We show that the given information is not enough by taking two cases:

 and 

 

 and  divide into , so  and .

 is prime and , so 

.

 

Therefore, if , (b) is greater, and if , (a) is greater.

Example Question #1 : How To Find The Least Common Multiple

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(a) and (b) are equal.

It is impossible to tell from the information given.

(a) is greater.

(b) is greater.

Correct answer:

(a) and (b) are equal.

Explanation:

The prime factorizations of 50 and 60 are:

The greatest common factor of 50 and 60 is the product of the prime factors they share:

The least common multiple of 50 and 60 is the product of all of the prime factors, with shared factors counted once:

,

(a) and (b) are equal.

Note: it is also a property of the integers that the product of the GCF and the LCM of two integers is equal to the product of the two integers themselves.

Example Question #452 : Isee Upper Level (Grades 9 12) Quantitative Reasoning

Which is the greater quantity?

(a) 

(b) 

Possible Answers:

(a) and (b) are equal

It is impossible to tell from the information given

(a) is greater

(b) is greater

Correct answer:

(a) is greater

Explanation:

(a) 

 

(b) To find , list their factors:

To find ,examine their prime factorizations:

                

                       

 

(a) is greater.

 

Example Question #2 : Least Common Multiple

Which of the following is the greater quantity?

(A) The least common multiple of 25 and 30

(B) 300

Possible Answers:

(B) is greater

(A) and (B) are equal

It is impossible to determine which is greater from the information given

(A) is greater

Correct answer:

(B) is greater

Explanation:

To find  we can list some multiples of both numbers and discover the least number in both lists:

, so (B) is greater

Example Question #3 : Least Common Multiple

Which of the following is the least common multiple of 25 and 40?

Possible Answers:

Correct answer:

Explanation:

List the first few multiples of both 25 and 40:

The least number in both lists of factors is 200.

 

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