6/( 1/ √ 12 + 1/√ 13 ) =
a)6/5
b)5/6
c)5
d)2√3 +3 √2
e)6√3−6√ 2
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GMATinsight
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BEST Method:sud21 wrote:6/( 1/ √ 12 + 1/√ 13 ) =
a)6/5
b)5/6
c)5
d)2√3 +3 √2
e)6√3−6√ 2
6/( 1/ √ 12 + 1/√ 13 ) = 6/(1/3.5 + 1/3.5) = 6/(0.3+0.3) = 6/0.6 = 10
Checking Options:
a)6/5 Close to 1.2 so nowhere close to 10 which is expected result of given expression
b)5/6 Close to 0.8 so nowhere close to 10 which is expected result of given expression
c)5 Nowhere close to 10 which is expected result of given expression
d)2√3 +3 √2 = 3.4+4.2=7.6 Closest Option
e)6√3−6√ 2 Close to 0 so nowhere close to 10 which is expected result of given expression
Answer: Option D
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GMATinsight
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Although I have eliminated other options to find best suitable option but these options still look Incorrect as the answer is nowhere close to 10 while checking any optionGMATinsight wrote:BEST Method:sud21 wrote:6/( 1/ √ 12 + 1/√ 13 ) =
a)6/5
b)5/6
c)5
d)2√3 +3 √2
e)6√3−6√ 2
6/( 1/ √ 12 + 1/√ 13 ) = 6/(1/3.5 + 1/3.5) = 6/(0.3+0.3) = 6/0.6 = 10
Checking Options:
a)6/5 Close to 1.2 so nowhere close to 10 which is expected result of given expression
b)5/6 Close to 0.8 so nowhere close to 10 which is expected result of given expression
c)5 Nowhere close to 10 which is expected result of given expression
d)2√3 +3 √2 = 3.4+4.2=7.6 Closest Option
e)6√3−6√ 2 = 6(1.7-1.4) Close to 1.8 so nowhere close to 10 which is expected result of given expression
Answer: Option D
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6/(1/√12 + 1/√13 ) = 6/(positive fraction) = MORE THAN 6.sud21 wrote:6/(1/√ 12 + 1/√ 13 ) =
a)6/5
b)5/6
c)5
d)2√3 + 3√2
e)6√3 − 6√2
Of the five answer choices, only D Is greater than 6.
The correct answer is D.
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√9 = 3 and √16 = 4sud21 wrote:6/( 1/ √ 12 + 1/√ 13 ) =
a)6/5
b)5/6
c)5
d)2√3 +3 √2
e)6√3−6√ 2
√12 is BETWEEN √9 and √16, so let's say √12 = APPROXIMATELY 3.5
Likewise, √13 is BETWEEN √9 and √16, so let's say √12 = APPROXIMATELY 3.5 also
Aside: As I will soon show, we need not be more accurate than this.
So, 6/(1/√12 + 1/√13 ) ≈ 6/(1/3.5 + 1/3.5 )
≈ 6/(2/3.5)
≈ (6)(3.5/2)
≈ (3)(3.5)
≈ 10.5
Before, we check the answer choices, it's important to note that everyone should memorize the following roots for test day:
√2 ≈ 1.4
√3 ≈ 1.7
√3 ≈ 2.2
a)6/5 too far from 10.5. ELIMINATE
b)5/6 too far from 10.5. ELIMINATE
c)5 too far from 10.5. ELIMINATE
d)2√3 + 3√2 = 5√2 ≈ (5)(1.4) = 7 This is the best answer
e)6√3 - 6√2 = Some negative value. too far from 10.5. ELIMINATE
Answer: D
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