Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 04 Aug 2015, 12:26

GMAT Club Expert Essay Review: Submit Yours Here

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

Author Message
Senior Manager
Joined: 02 Nov 2008
Posts: 283
Followers: 1

Kudos [?]: 52 [0], given: 2

00:00

Difficulty:

(N/A)

Question Stats:

100% (01:39) correct 0% (00:00) wrong based on 6 sessions
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

(sqrt(9 +sqrt80) + sqrt(9-sqrt80))^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

Last edited by chicagocubsrule on 17 Nov 2009, 15:10, edited 1 time in total.
VP
Joined: 05 Mar 2008
Posts: 1473
Followers: 11

Kudos [?]: 221 [0], given: 31

chicagocubsrule wrote:
((9^(1/2) +80^(1/4)) +(9^(1/2) – 80^(1/4)) ^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

I keep getting 36..are you sure this is correct?

I double-checked with google calculator and it too got 36

VP
Joined: 05 Mar 2008
Posts: 1473
Followers: 11

Kudos [?]: 221 [0], given: 31

chicagocubsrule wrote:
((9^(1/2) +80^(1/4)) +(9^(1/2) – 80^(1/4)) ^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

but question should read (sqrt(9 +sqrt80) + sqrt(9-sqrt80))^2
Senior Manager
Joined: 02 Nov 2008
Posts: 283
Followers: 1

Kudos [?]: 52 [0], given: 2

lagomez wrote:
chicagocubsrule wrote:
((9^(1/2) +80^(1/4)) +(9^(1/2) – 80^(1/4)) ^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

but question should read (sqrt(9 +sqrt80) + sqrt(9-sqrt80))^2

my mistake (I've edited my original post)...answer is 20...can you please explain?
VP
Joined: 05 Mar 2008
Posts: 1473
Followers: 11

Kudos [?]: 221 [0], given: 31

chicagocubsrule wrote:
lagomez wrote:
chicagocubsrule wrote:
((9^(1/2) +80^(1/4)) +(9^(1/2) – 80^(1/4)) ^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

but question should read (sqrt(9 +sqrt80) + sqrt(9-sqrt80))^2

think of (a+b)^2 = a^2 + 2ab + b^2

let's say a = sqrt(9 + sqrt80)
so that squared = 9 + sqrt 80

b = sqrt(9-sqrt80) and that squared = 9 - sqrt 80

2ab
= 2(sqrt(9+sqrt80)*sqrt(9-sqrt80)
=2((9+sqrt80)(9-sqrt80))
=2(81+80)
=2(1)
=2

combing all we get:
9 +sqrt80 + 9 - sqrt80 + 2 = 20
Senior Manager
Affiliations: PMP
Joined: 13 Oct 2009
Posts: 312
Followers: 4

Kudos [?]: 117 [0], given: 37

chicagocubsrule wrote:
(sqrt(9 +sqrt80) + sqrt(9-sqrt80))^2
The square root of the sum of 9 and the square root of 80 plus the square root difference (so subtraction) between 9 and the square root of 80 (so the 9’s are under one radical (initial square root) and the 80’s are under 2 radicals.
a) 1
b) 9 – 4(5)^1/2
c) 14
d) 18
e) 20

Chicago - it would be easier to read if u use "m"

reading the question itself took half of my energy - LOL

BTW I got 20 too

here we are applying the formulas
$$(a+b)^2 = a^2+2ab+b^2$$
and
$$(a+b)(a-b) = a^2-b^2$$
_________________

Thanks, Sri
-------------------------------
keep uppp...ing the tempo...

Press +1 Kudos, if you think my post gave u a tiny tip

Display posts from previous: Sort by