time taken to complete the journey= 10 hour
time taken in first half= 10km/hr
=50km in 5hr
time taken in second half = 15 km / hr
= 75km in 5 hr
therefore Total distance covered =50+75=125km in 10 hr
the law of definite proportion, sometimes called proust's law or the law of definite composition, or law of constant composition states that a given chemical compound always contains its component elements in fixed ratio and does not depend on its source and method of preparation.