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

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Intern
Joined: 03 Apr 2015
Posts: 10

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Updated on: 13 Dec 2017, 08:16
3
00:00

Difficulty:

45% (medium)

Question Stats:

61% (01:52) correct 39% (01:51) wrong based on 109 sessions

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

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

LBS Simulator - Economist

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

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

The correction says to focus on the Quadratic equation!

Help me
Daniela

_________________

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.
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Math Expert
Joined: 02 Sep 2009
Posts: 48097

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

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

LBS Simulator - Economist

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

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

The correction says to focus on the Quadratic equation!

Help me
Daniela

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

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

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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Math Expert
Joined: 02 Sep 2009
Posts: 48097

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

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

LBS Simulator - Economist

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

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:

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

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