GRE - Quantitative Comparisons

Approach

Compare, and if simple, calculate

 Reduce within the columns – make one column look like the other

                         Column A                  Circle with Area 9תּ             Column B

                  r                                                                     d ÷ 2

Solution:  The area of a circle is תּr2, so a circle with an area of 9תּ has a radius of 3.  Did you need to go through that?  No!  You already know that the radius of a circle is one-half of the diameter!  These are equal!

 Reduce between the columns – add, subtract, multiply, or divide by common terms

Column A                     5y + 9  =  3z - 2              Column B

                         20y + 28                                                            12z - 16

Solution:  How can you reduce these?  Everything is a multiple of 4, so try dividing by 4 to get A: 4(5y + 7) and B: 4(3z - 4).  If you drop the fours, you end up with A: 5y + 7 and B: 3z - 4, which still doesn't look like the stem.  If you add 2 to each side, however, you get exactly the stem equation!  These are equal!

  Plug in numbers – ALWAYS trying with more than one number

Column A                                                          Column B

                    Square root of 49                                                           7

Solution:  Don't be tempted!  7 x 7 is indeed 49, but so is -7 x -7!  You can't determine this relationship!

Draw any diagrams, exaggerating angles and/or dimensions

                     

 

Cautions

 Don’t assume anything!

Don’t hurry and be mislead!

Don’t stop at your first answer

  • Try a much smaller or larger number

  • Try a fraction

  •  Try a negative number

 Remember your basic math rules – they’ll be your best friend here!

Structure

The problem will have two columns, A and B.  There may also be an equation and/or information centered above these columns that applies to both.

Column A                       5 – x  =  3 + x              Column B

      x                                                                       2

Answer Choices

A)  The quantity in Column A is greater

B)  The quantity in Column B is greater

C)  The two quantities are equal

D)  The relationship cannot be determined from the information given

(hint:  if both columns are numbers, D can never be correct)