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# k is a positive number. If k is twice its reciprocal, and j is twice k

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Math Expert
Joined: 02 Sep 2009
Posts: 51184
k is a positive number. If k is twice its reciprocal, and j is twice k  [#permalink]

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23 Aug 2018, 22:37
00:00

Difficulty:

15% (low)

Question Stats:

83% (00:50) correct 17% (01:05) wrong based on 48 sessions

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k is a positive number. If k is twice its reciprocal, and j is twice k, then jk =

A. 2√2
B. 4
C. 4√2
D. 8
E. 8√2

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k is a positive number. If k is twice its reciprocal, and j is twice k  [#permalink]

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23 Aug 2018, 22:42
Given K = 2($$\frac{1}{K}$$).

$$K^2$$ = 2.

K = $$\sqrt{2}$$

Now J = 2K
J = 2$$\sqrt{2}$$.

JK = $$\sqrt{2}$$*2$$\sqrt{2}$$

JK = 4.

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Re: k is a positive number. If k is twice its reciprocal, and j is twice k  [#permalink]

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23 Aug 2018, 22:44
Bunuel wrote:
k is a positive number. If k is twice its reciprocal, and j is twice k, then jk =

A. 2√2
B. 4
C. 4√2
D. 8
E. 8√2

Given k=2*(1/k)
Or, k^2=2

Given j=2*k

So, j*k=2k*k=2k^2=2*2=4

Ans. (B)

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k is a positive number. If k is twice its reciprocal, and j is twice k  [#permalink]

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24 Aug 2018, 02:38
Bunuel wrote:
k is a positive number. If k is twice its reciprocal, and j is twice k, then jk =

A. 2√2
B. 4
C. 4√2
D. 8
E. 8√2

k = 2* $$\frac{1}{k}$$
j = 2k

jk = 2k* 2 *$$\frac{1}{k}$$

jk = 4.

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Re: k is a positive number. If k is twice its reciprocal, and j is twice k  [#permalink]

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24 Aug 2018, 07:08
Bunuel wrote:
k is a positive number. If k is twice its reciprocal, and j is twice k, then jk =

A. 2√2
B. 4
C. 4√2
D. 8
E. 8√2

The number is $$k$$ ; its reciprocal is $$\frac{1}{k}$$

$$k = \frac{2}{k}$$

Or, $$k^2 = 2$$

So, $$k = \sqrt{2}$$

$$k = 2\sqrt{2}$$

So, $$jk = \sqrt{2}*2\sqrt{2}$$

Or, $$jk = 4$$, Answer must be (B)
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Re: k is a positive number. If k is twice its reciprocal, and j is twice k &nbs [#permalink] 24 Aug 2018, 07:08
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