DE = BC = 3000 m
i.e. the plane travels a distance of 3000m in 15 seconds
\therefore the speed of the plane =\frac{\text { distance }}{\text { time }}=\frac{3000}{15}=200 \mathrm{m} / \mathrm{s}
=200 \times \frac{18}{5} \mathrm{km} / \mathrm{hr}
= 720km/hr
Hence, the speed of the aeroplane is 720km/hr.
KC Sinha: Exercise 9.1 – Mathematics Solution Class 10 Chapter 9 Some Applications of Trigonometry
