A die is thrown 240 times and a 6 turns up 30 times test if the die is biased.

The answer given is no due to the test statistic being -1.73 but frankly i cant see this as i get $\displaystyle \sqrt{6}$ not $\displaystyle \sqrt{3}$ from $\displaystyle \frac{\frac{30}{120}-\frac{1}{6}}{\sqrt{\frac{\frac{1}{6}\frac{5}

{6}}{120}}}=z$ any ideas?