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If the operation @ is defined (OG16)

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boomgoesthegmat Senior | Next Rank: 100 Posts Default Avatar
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If the operation @ is defined (OG16)

Post Thu May 19, 2016 3:46 pm
If the operation @ is defined by x @ y = sqrt(xy) for all positive numbers x and y, then (5 @ 45) @ 60 =

A) 30
B) 60
C) 90
D) 30sqrt(15)
E) 60sqrt(15)

OA: A

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Top Reply
Post Thu May 19, 2016 4:04 pm
boomgoesthegmat wrote:
If the operation @ is defined by x @ y = √(xy) for all positive numbers x and y, then (5 @ 45) @ 60 =

A) 30
B) 60
C) 90
D) 30√15
E) 60√15

OA: A
I call these "Strange Operator" questions.
We want to evaluate: (5 @ 45) @ 60

Start with (5 @ 45)
(5 @ 45) = √[(5)(45)]
= √225
= 15


So, (5 @ 45) @ 60 = 15 @ 60
From here, 15 @ 60 = √[(15)(60)]
= √900
= 30

Answer: A

RELATED RESOURCE (video)
- Strange operators: https://www.gmatprepnow.com/module/gmat-algebra-and-equation-solving/video/976
- Additional practice: https://www.gmatprepnow.com/module/gmat-algebra-and-equation-solving/video/977

Cheers,
Brent

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