Question

A man can row 8 km/hr in still water and speed of stream is 2 km/hr. If it will take 2 hours more to travel upstream the same distance than downstream, then what will be the distance travelled during downstream?
1. 30 km
2. 20 km
3. 45 km
4. 50 km
5. 35 km

Answer 1

Correct Answer - Option 1 : 30 km

Given:

Speed of boat in still water = 8 km/hr

Speed of stream = 2 km/hr

Difference of time taken during upstream and downstream = 2 hours

Concept used:

Downstream speed (S_D) = Speed of boat + Speed of stream

Upstream speed (S_U) = Speed of boat – Speed of stream

T_D = D_D/S_D

T_U = D_U/S_U

Calculation:

Let the distance travelled during upstream be D km

Distance travelled during downstream = D km

S_D = 8 + 2 = 10 km/hr

S_U = 8 – 2 = 6 km/hr

T_D = D/SD 

⇒ TD = D/10

T_U = D/SU  

⇒ T_U = D/6

According to question

T_U – T_D = 2

⇒ D/6 – D/10 = 2

⇒ 2D/30 = 2

⇒ D = 30 km

∴ Distance travelled during downstream is 30 km