Question:
Which of the following is irrational?
(a) $\sqrt{\frac{4}{9}}$
(b) $\sqrt{\frac{4}{5}}$
(c) $\sqrt{7}$
(d) $\sqrt{81}$
Solution:
Given that
$\sqrt{\frac{4}{9}}=\frac{2}{3}$
$\frac{4}{5}=0.8$
$\sqrt{81}=9$
And 7 is not a perfect square.
Hence the correct option is
.