Statistics and Probability: dispersion

Appropriate measure: Bowley's (quartile) coefficient of skewness, because the last class is the most frequent, so the mode cannot be located reliably.

$N=172$.

$Q_1$: $\frac N4=43$, class $20$-$30$: $Q_1=20+\dfrac{43-22}{25}\times10=28.4$

$Q_2$: $\frac N2=86$, class $40$-$50$: $Q_2=40+\dfrac{86-82}{40}\times10=41$

$Q_3$: $\frac{3N}{4}=129$, class $50$-$60$: $Q_3=50+\dfrac{129-122}{50}\times10=51.4$

$S_k=\frac{Q_3+Q_1-2Q_2}{Q_3-Q_1}=\frac{51.4+28.4-82}{51.4-28.4}=\frac{-2.2}{23}\approx-0.096$

Since $S_k<0$, the distribution is (slightly) negatively skewed.