Starting in November 2007, your GRE Quantitative Ability section might include one numeric-entry question, in which you enter a number response using the keyboard instead of selecting among multiple choices. The problem might call for you to enter a single decimal number, either positive or negative (for example, 125 or -14.2), or it might call for you to enter a fraction by typing a numerator in one box and typing a denominator below it, in another box.

NOTE: For more information on the 2007 test changes, see Revisions to the General GRE (November 2007 and beyond).

 
Sample Question

If 2x + 1 is a multiple of 5, and if 2x + 1 < 100, how many possible values of x are prime numbers? Click on the answer box, then type a number. Backspace to erase.

QuickTip:

Start plugging in numbers for x that work in the equation, and keep going until you see a pattern that allows you to get to the answer as quickly as possible.

Analysis

Work your way up from the lowest possible value of x. Substitute numbers for x that work in the equation (numbers for which the equations holds). As you work your way up in the value of x, you should begin to see a pattern:

2(2) + 1 = 5
2(4.5) + 1 = 10
2(7) + 1 = 15
2(9.5) + 1 = 20
2(12) + 1 = 25

Notice that as the sum increase in multiples of 5, the value of x in every second equation is an integer that also increases in multiples of 5, and this integer ends in either digit 2 or 7. No integer ending in 2 (other than 2 itself) is a prime number. So you need only consider the prime number 2 along with values of x ending in 7 and less than 49 (the question stipulates that 2x + 1 < 100):

{2, 7, 17, 27, 37, 47}

Five of these integers — 2, 7, 17, 37, and 47 — are prime numbers. Therefore, to receive credit for answering the question correctly, you must type the number 5 in the numeric-entry box.