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Simplification & Approximation · Question 47 of 71

Question 47

MediumOriginal question

Evaluate (278)−23\left(\frac{27}{8}\right)^{-\frac{2}{3}}.

Options for question 47

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. The negative sign flips the fraction: (827)23\left(\frac{8}{27}\right)^{\frac{2}{3}}.

  2. The 3 in the denominator of the power means cube root: 8273=23\sqrt[3]{\frac{8}{27}} = \frac{2}{3}.

  3. The 2 means square: (23)2=49\left(\frac{2}{3}\right)^2 = \frac{4}{9}.

Worth noting

Ignoring the minus sign gives 94\frac{9}{4}; stopping after the cube root gives 23\frac{2}{3}.

Concept
Negative fractional indices
Typical time
50 s
Your time
—
The rule this testsPowers, roots and surds
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Ten questions from Simplification & Approximation, at your own pace.

Practise this chapter →

Ten questions from Simplification & Approximation, at your own pace.