Correct Answer - Option 2 : (8, 12) hours
Given∶
Distance = 640 km
Speed on uphill = 20 km/hr
Speed on down hill = 40 km/hr
Time = 20 hours
Formula Used∶
Concept of Linear Equations, Distance = Speed × Time
Calculation∶
Let the time takes for uphill journey = x hrs
time takes for downhill journey = y hrs
∴ x + y = 20
and 20x + 40y = 640
Solving above equations, we get
20y = 240
⇒ y = 240/20 = 12 and
x + 12 = 20
⇒ x = 20 - 12 = 8
∴ Time taken for Uphill journey is 8 hours and for Down hill journey is12 hours.