Given :
Xinran walks 3 mi/h uphill, 4 mi/h on flat land and 5 mi/h downhill.
To Find :
If he walks one mile uphill, then one mile on flat land and then returns by the same route to his starting point, how many minutes does he walk.
Solution :
Time taken to walk one mile uphill is :
[tex]t_1 = \dfrac{1}{3}\ hours[/tex]
Time taken to walk two mile on flat land( one on going and one or returning ) is :
[tex]t_2 = \dfrac{2}{4}\ hours\\\\ t_2 = \dfrac{1}{2}\ hours[/tex]
Time taken to walk one mile downhill is :
[tex]t_3 = \dfrac{1}{5}\ hours[/tex]
Total time taken :
[tex]T = t_1 + t_2 + t_3 \\\\T = \dfrac{1}{3} + \dfrac{1}{2}+\dfrac{1}{5}\\\\T = \dfrac{10 + 15 + 6}{30} \\\\T = \dfrac{31}{30}\ hours = \dfrac{31}{30}\times 60 \ minutes\\\\T = 62\ minutes[/tex]
Therefore, time taken un 62 minutes.
