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(3p + 1)(3p – 1)

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GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1650 [0], given: 396

(3p + 1)(3p – 1) [#permalink]  06 Apr 2018, 15:23
Expert's post
00:00

Question Stats:

92% (00:22) correct 7% (00:17) wrong based on 13 sessions
 Quantity A Quantity B $$(3p + 1)(3p - 1)$$ $$9p^2$$

A. Quantity A is greater.
B. Quantity B is greater.
C. The two quantities are equal.
D. The relationship cannot be determined from the information given.

Drill 1
Question: 1
Page: 507
[Reveal] Spoiler: OA

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Sandy
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Manager
Joined: 26 Jan 2018
Posts: 172
Followers: 0

Kudos [?]: 104 [1] , given: 3

Re: (3p + 1)(3p – 1) [#permalink]  08 Apr 2018, 01:35
1
KUDOS
(a+b)(a-b)=a^2-b^2

(3p + 1)(3p - 1)= 9p^2-1

This is everytime less than 9p^2 as 1 is deducted from it irrespective of it's value. This also hold good even if the number is a fraction or some integer.
GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1650 [0], given: 396

Re: (3p + 1)(3p – 1) [#permalink]  15 Apr 2018, 05:22
Expert's post
Explanation

Evaluate the relationship between the quantities by plugging in values for p: Try p = 2.

Quantity A is 7 × 5 = 35, and Quantity B is 9 × 4 = 36; Quantity B is greater, so eliminate choices (A) and (C). Any value gives the same outcome, so select answer choice (B). Algebraically, you could either FOIL Quantity A or recognize the common quadratics—either way, Quantity A simplifies to 9p2 – 1, which is always exactly 1 less than Quantity B.
_________________

Sandy
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Re: (3p + 1)(3p – 1)   [#permalink] 15 Apr 2018, 05:22
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