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Spaceland Prep Strategy Question #4

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by spaceland prep » Thu Mar 10, 2011 9:25 am
Q. What is the range of values of b for which 1 - b^8 < 0 ?

(A) b < -1 or b > 1
(B) -1 <= b <= 1
(C) b > = 1
(D) b <= -1
(E) 0 <= b <= 1

Which answer choices complement one another--meaning they aggregately describe the entire range of numbers? How does recognizing this occurrence help?

Solution

[spoiler]Answer choices (A) and (B) cover the whole range of numbers. This is significant because the GMAT questions tend to be answered by one of the complementary answers.

In this particular case, answer (A) is correct.

Occasionally you'll find some answer choices combine to describe all the numbers that a solution could contain. Knowing that the GMAT typically makes one of these answers the correct one can save you time.

A similar phenomenon occurs frequently with probability problems, percent problems and proportion problems. When answers on these problems add up to 1 or 100% often times one of those answers is the correct one.[/spoiler]
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Source: — Problem Solving |

by force5 » Thu Mar 10, 2011 9:50 am
consider this question like this

1-b^8<0
then
b^8>1 which means that b can never be equal to 1 ( because @b=1, b^8 =1)
further
we know that b will lie between 1 and -1 ( inequality rule)

hence answer (A). the writer has made answer choices very easy by writing b = 1 in all cases except A. ( b can never be 1)

hope that helps
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