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Which of the numbers \(\frac{\sqrt{5}}{2}\), \(\sqrt{\frac{5}{2} }\), \(\frac{2}{\sqrt{5}}\) \(\sqrt{\frac{2}{5} }\), and \(\frac{1}{\sqrt{5}}\) is the greatest?

A. \(\frac{\sqrt{5}}{2}\),

B. \(\sqrt{\frac{5}{2} }\)

C. \(\frac{2}{\sqrt{5}}\)

D. \(\sqrt{\frac{2}{5} }\)

E. \(\frac{1}{\sqrt{5}}\)

The question aims to test approximation techniques

\(\frac{\sqrt{5}}{2}\)

\(\sqrt{5} \approx 2.25\)

\(\frac{\sqrt{5}}{2} \approx 1.1\)

\(\sqrt{\frac{5}{2} }\)

\(\sqrt{2.5}\)

\(1.5 * 1.5 = 2.25\)

\(\sqrt{2.5} \approx 1.5\) ⇒ The actual value will be greater than 1.5

\(\frac{2}{\sqrt{5}}\)

\(\frac{2}{2.25} \approx 0.XX\) ⇒ The value will lie between 0 and 1

\(\sqrt{\frac{2}{5} }\)

\(\sqrt{0.4} \approx 0.XX\) ⇒ The value will lie between 0 and 1

\(\frac{1}{\sqrt{5}}\)

\(\approx \frac{1}{2.5} \approx 0.XX\) ⇒ The value will lie between 0 and 1

Highest value = \(\sqrt{\frac{5}{2} }\)

Option B
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Bunuel
Which of the numbers \(\frac{\sqrt{5}}{2}\), \(\sqrt{\frac{5}{2} }\), \(\frac{2}{\sqrt{5}}\) \(\sqrt{\frac{2}{5} }\), and \(\frac{1}{\sqrt{5}}\) is the greatest?

A. \(\frac{\sqrt{5}}{2}\),

B. \(\sqrt{\frac{5}{2} }\)

C. \(\frac{2}{\sqrt{5}}\)

D. \(\sqrt{\frac{2}{5} }\)

E. \(\frac{1}{\sqrt{5}}\)


Another method would be to get all under square roots.

A. \(\frac{\sqrt{5}}{2}=\sqrt{\frac{5}{4}}\),

B. \(\sqrt{\frac{5}{2} }\)

C. \(\frac{2}{\sqrt{5}}=\sqrt{\frac{4}{5}}\)

D. \(\sqrt{\frac{2}{5} }\)

E. \(\frac{1}{\sqrt{5}}=\sqrt{1/5}\)

Now compare what is under the square root = 5/4, 5/2, 4/5, 2/5 and 1/5.

5/2 is the highest so it’s square will also be the highest.


B
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I did something completely different from the answers provided.

I multiplied each option with a fraction so that the denominator became 2√5 for all the options.
A) √5/2 * √5/√5 = 5/2√5
B) √5/√2 * √2√5/√2√5 = 5√2/2√5
C) 2/√5 * 2/2 = 4/2√5
D) √2/√5 * 2/2 = 2√2/2√5
E) 1/√5 * 2/2 = 2/2√5

Now the option with the greatest value in the numerator becomes the greatest fraction.

We can eliminate A, D, E.

Now, numerator B) 5*√2 is > C) 4.

Therefore, answer is B).
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This can be solved by taking the LCM of all the denominators. The LCM will be 2*sq root (5).

Now when you compare the numerators in each fraction with a common denominator, You will get (B)
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Multiply each option by root over 5.

They will be :-

5/2 , 5/ root 2 , 2 , root 2 and 1

root 2 = 1.4
Hence , 5 / root 2 = 5 / 1.4 = 5 *10 / 14 = 5*10 / 15 = 10/ 3 = 3.33

Hence B is answer.
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I solved it by comparing,
Fist compare A and B, both have same numerator, so lower the denominator higher the value, √(5/2) >√5/2
Similarly compare C, D & E, here they have same denominator so greatest numerator will have greatest value so it's clearly C , 2/√5
Finally compare B and C by cross multiplication, 5>2√2
Hence its B
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