Question

Tyler and Pearl went on a 20km bike ride that lasted for 3 hours. Because of steep hills or the trail, they walked for most of the trip. Their walking speed was 4km/hr. Their riding speed was 12km/hr. How much time did they spend walking?

Answer 1

Answer: 1 hour

Step-by-step explanation:

Let the distance they walked be $d_1$ in time $t_1$ and the distance they walked be $d_2$ in time $t_2$ ,then

Walking speed=$\frac{d_1}{t_1}=4$

$\\\Rightarrow\ d_1=4t_1$

Riding speed=$\frac{d_2}{t_2}=12$

$\\\Rightarrow\ d_2=12t_1$

Also the total time taken=3 hours

∴$t_1+t_2=3\\\Rightarrow\ t_2=3-t_1$...(1)

Since the total distance= 20 km

∴$d_1+d_2=20\\\Rightarrow4t_1+12t_2=20\\\Rightarrow4t_1+12(3-t_1)=20..............[\text{from (1)}]\\\Rightarrow4t_1+36-12t_1=20\\\Rightarrow-8t_1=-8\\\Rightarrow\ t_1=1$

Thus, the they spent 1 hour time in walking.