Question

which number is irrational and why?

$\sqrt{ \frac{4 }{9} }$
$\sqrt{20}$
$\sqrt{121}$

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Answer 1

The answer is the second choice: √20

Explanation:

It is irrational. It simplifies to 2√5, but this is also irrational. To be rational, the decimal would have to be able to be written as a fraction. This radical, both 20 and 5, is a non-terminating and non-repeating decimal, so it cannot be written as a fraction.