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((80+25)^2-8000)^(1/2)

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Joined: 03 Apr 2015
Posts: 10
Concentration: General Management, International Business
((80+25)^2-8000)^(1/2) [#permalink]

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New post Updated on: 13 Dec 2017, 08:16
3
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A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

61% (01:59) correct 39% (01:45) wrong based on 95 sessions

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\(\sqrt{(80+25)^2-8000}\)

A. 25
B. 45
C. 55
D. 45^2
E. 55^2

[Reveal] Spoiler:
LBS Simulator - Economist

How would you answer the question?
√(105^2-8000)
=√(11000-8000)
=√(3000)
=over 50 (because √(2500)=50)


Answer= C

I estimated but I wanted to know to to actually solve it.

The correction says to focus on the Quadratic equation!

Help me
Daniela
[Reveal] Spoiler: OA

_________________

Daniela

From 330 - Doing my best to beat the gmat!!


Originally posted by dmatinho on 13 Dec 2017, 08:08.
Last edited by Bunuel on 13 Dec 2017, 08:16, edited 1 time in total.
Renamed the topic and edited the question.
Economist GMAT Tutor Discount CodesMath Revolution Discount CodesMagoosh Discount Codes
Expert Post
Math Expert
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V
Joined: 02 Sep 2009
Posts: 44623
Re: ((80+25)^2-8000)^(1/2) [#permalink]

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New post 13 Dec 2017, 08:33
dmatinho wrote:
\(\sqrt{(80+25)^2-8000}\)

A. 25
B. 45
C. 55
D. 45^2
E. 55^2

[Reveal] Spoiler:
LBS Simulator - Economist

How would you answer the question?
√(105^2-8000)
=√(11000-8000)
=√(3000)
=over 50 (because √(2500)=50)


Answer= C

I estimated but I wanted to know to to actually solve it.

The correction says to focus on the Quadratic equation!

Help me
Daniela


\(\sqrt{(80+25)^2-8000}=\sqrt{105^2-8000}=\sqrt{5^2*21^2-5^2*320}=5\sqrt{21^2-320}=\)

\(=5\sqrt{441-320}=5\sqrt{121}=5*11=55\).

Answer: C.

P.S. Please follow the rules when posting a question: https://gmatclub.com/forum/rules-for-po ... 33935.html Thank you.
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Expert Post
Math Expert
User avatar
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Joined: 02 Sep 2009
Posts: 44623
((80+25)^2-8000)^(1/2) [#permalink]

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New post 13 Dec 2017, 08:43
dmatinho wrote:
\(\sqrt{(80+25)^2-8000}\)

A. 25
B. 45
C. 55
D. 45^2
E. 55^2

[Reveal] Spoiler:
LBS Simulator - Economist

How would you answer the question?
√(105^2-8000)
=√(11000-8000)
=√(3000)
=over 50 (because √(2500)=50)


Answer= C

I estimated but I wanted to know to to actually solve it.

The correction says to focus on the Quadratic equation!

Help me
Daniela


Or another way:

\(\sqrt{(80+25)^2-8000}=\sqrt{6400+4000+625-8000}=\sqrt{3025}=55\).

Answer: C.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

((80+25)^2-8000)^(1/2)   [#permalink] 13 Dec 2017, 08:43
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