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a*b = ab/(a + b) for all a, b that satisfy a ≠ -b. What is the value

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a*b = ab/(a + b) for all a, b that satisfy a ≠ -b. What is the value  [#permalink]

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New post 22 Jul 2019, 01:32
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

88% (00:30) correct 12% (00:39) wrong based on 25 sessions

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a*b = ab/(a + b) for all a, b that satisfy a ≠ -b. What is the value  [#permalink]

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New post 22 Jul 2019, 02:36
Bunuel wrote:
\(a \circ b = \frac{ab}{a+b}\) for all a, b that satisfy \(a ≠ -b\). What is the value of \((–4) \circ 2\)?

A. \(-4\)

B. \(-2\)

C. \(-\frac{4}{3}\)

D. \(\frac{4}{3}\)

E. \(4\)


Given: \(a \circ b = \frac{ab}{a+b}\) for all a, b that satisfy \(a ≠ -b\).
Asked: What is the value of \((–4) \circ 2\)?

\((–4) \circ 2 = \frac{(-4)*2}{-4+2}= \frac{-8}{-2} = 4\)

IMO E
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Re: a*b = ab/(a + b) for all a, b that satisfy a ≠ -b. What is the value  [#permalink]

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New post 23 Jul 2019, 04:34

Solution


Given:
    • \(a ∘ b = \frac{ab}{a+b}\)
    • a ≠ −b

To find:
    • The value of (–4)∘2

Approach and Working Out:
    • \((–4)∘2 = \frac{-4*2}{(-4 + 2)} = \frac{-8}{-2} = 4\)

Hence, the correct answer is Option E.

Answer: E

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Re: a*b = ab/(a + b) for all a, b that satisfy a ≠ -b. What is the value   [#permalink] 23 Jul 2019, 04:34
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