Given \(\mu=1.42, A=10^{\circ}, \mu^{\prime}=1.7, A^{\prime}=?\)

\(\therefore \quad(1.42-1) \times 10=(1.7-1) A^{\prime}\)

\((0.42) \times 10=0.7 \times A^{\prime}\)

or \(\quad A^{\prime}=\frac{0.42 \times 10}{0.7}=6^{\circ}\)