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            GMAT Sample Questions & Answers

            GMAT sample questions and answers written by our admissions experts

            D. y(x + z)

            E. z(x + y)

            Answer:

            Method 1: Algebraic Approach

            As we are dealing with numbers greater than 1, there are 2 rules that must be noted:

            • The product of two numbers is greater than each one of them;

            • The larger the numbers, the larger the product

            Thus if 1 < x < y < z, we can derive the following inequailities:

            • xy < xz < yz

            • x < y < z < xz

            When we open up the multiplications on each alternative:

            A. z(x + 1) = xz + z
            B. z(y + 1) = yz + z
            C. x(y + z) = xy + xz
            D. y(x + z) = xy + yz
            E. z(x + y) = xz + yz

            We have the following conclusions:

            1. (B) is greater than (A) as yz > xz

            2. Comparing (C), (D) and (E), (E) will be the greatest, as xy < xz < yz

            3. (E) is greater than (B), as xz > z

            Answer (E)

            Method 2: Plug-in numbers

            Recalling the fact that the GMAT doesn’t regard the workings towards the correct answer, we could experiment with numbers instead of letters, since the alternatives have to be true for any values of x, y and z, as long as the condition 1 < x < y < z is respected:

            Let’s try with x = 2, y = 3 and z = 4 and check which alternative gives us the largest number:

            A. z(x + 1) = 4(2 + 1) = 4 × 3 = 12
            B. z(y + 1) = 4(3 + 1) = 4 × 4 = 16
            C. x(y + z) = 2(3 + 4) = 2 × 7 = 14
            D. y(x + z) = 3(2 + 4) = 3 × 6 = 18
            E. z(x + y) = 4(2 + 3) = 4 × 5 = 20

            And we can quickly spot (E) as the correct alternative!


            Problem solving: Quant, Quantitative, Estimation


            Question:

            Over the past 7 weeks, the Smith family had weekly grocery bills of $74, $69, $64, $79, $64, $84, and $77. What was the Smiths' average (arithmetic mean) weekly grocery bill over the 7-week period?

            A. $64

            B. $70

            C. $73

            D. $74

             E. $85

            Answer:

            Method 1: The regular Approach

            It’s quite well known that average of a set of numbers is the sum of those numbers divided by the quantity of those numbers. In our case we have:

            Average = (74 + 69 + 64 + 79 + 64 + 84 + 77)÷7

            While this is a straight-forward problem, performing 74 + 69 + 64 + 79 + 64 + 84 + 77 without a calculator will be time-consuming job during which distractions could most likely happen!

            At any rate, since: 74 + 69 + 64 + 79 + 64 + 84 + 77=511

            And 511 ÷ 7 = 73

            Answer (C)

            Method 2: Estimations Method

            An alternative approach to decrease the amount of calculations with “big numbers” is to estimate (guess) what the average would be and add it to the average of the differences of every number

            Let’s say that, from glancing at the numbers in the question, one would estimate their average to be 75. 

            Let’s calculate the differences between each number and 75

            74 – 75 = -1

            69 – 75 = -6

            64 – 75 = -11

            79 – 75 = 4

            64 – 75 = -11

            84 – 75 = 9

            77 – 75 = 2

            Since the sum of -1, -6, -11, 4, -11, 9 and 2 will be -14 and -14 ÷ 7 = -2, it comes out that the average of the differences is -2.

            Therefore 75 - 2 = 73  – the correct answer is C!


            These questions have been written by Cara Skikne and Shimon Goldchmit.