A tortoise moves a distance of 100 metres in 15 minutes. What is the average speed of tortoise in km/h ?
Total distance $$=100\,m =0.1 \,km$$
Total time taken $$=15\, minutes = 15/60=0.25\, hour$$
Average speed = $$\dfrac{Total\ distance\ travelled}{ Total\ time\ taken}$$
$$=\dfrac{0.1}{0.25}= 0.4\, km/h$$