Each side of right triangle DEF is an integer. Which of the following, if known, would yield exactly one area for triangle DEF?

# Archive | Math Brain Twister

## Brain Twister – Prime Factorials (Answer)

Happy Thursday! Here’s a look back at Monday’s GRE Brain Twister! 13! – 11! is divisible by n but not by n^2. What is the range of values of n if n is a prime number? (A) 20 (B) 24 (C) 26 (D) 29 (E) 31 Explanation The first step is to factor this […]

## Brain Twister – Prime Factorials

Here’s the latest GRE Brain Twister! Be sure to come back this Thursday for the answer and explanation! 😀 13! – 11! is divisible by n but not by n^2. What is the range of values of n if n is a prime number? (A) 20 (B) 24 (C) 26 (D) 29 (E) 31

## GRE Brain Twister: Mammoth Exponents (Answer)

If a and b are positive integers, what is the greatest possible value of a? (A) 2 (B) 5 (C) 10 (D) 11 (E) 13 Explanation Though you might be tempted to run for your calculator, this problem can be solved using a couple of logic-based approaches. Indeed, no intense calculation needed, just some […]

## GRE Brain Twister: Mammoth Exponents

If a and b are positive integers, what is the greatest possible value of a? (A) 2 (B) 5 (C) 10 (D) 11 (E) 13

## GRE Brain Twister: Non-Standard Deviation (Answer)

Here’s the answer to this week’s GRE Brain Twister! Set A consists of five positive numbers. SAT B consists of the square roots of each of the five numbers from Set A. If the standard deviation of Set B > standard deviation of Set A, which of the following must be true? I. The range […]

## GRE Brain Twister: Non-Standard Deviations

Set A consists of five positive numbers. SAT B consists of the square roots of each of the five numbers from Set A. If the standard deviation of Set B > standard deviation of Set A, which of the following must be true? I. The range of the numbers in Set A is greater than […]

## GRE Brain Twister: A Prime Example (Answer)

Here’s the answer from Monday’s Brain Twister! A math teacher assigns a distinct prime number, starting with the lowest, for each student in her class. If she chooses two students at random, the probability the sum of their numbers is not even is less than 1/10. What is the fewest possible number of students in […]

## GRE Brain Twister: A Prime Example

Here’s this month’s GRE Brain Twister! Try to answer it in the comments below, and we’ll post the answer on Thursday! A math teacher assigns a distinct prime number, starting with the lowest, for each student in her class. If she chooses two students at random, the probability the sum of their numbers is not […]

## GRE Brain Twister – Watch out for the Trap(ezoid)! (Answer)

Here’s the answer to Monday’s Brain Twister! *Figure not drawn to scale Given that angle ACD and angle BDC are less than 90, what is the smallest possible area of trapezoid ABCD* in which the height each side is a different integer length? Explanation: A good way to get the answer is to play around […]