Originally Posted by

**tommylai12** A man in a boat is 3 km from O, which is the nearest point in straight beach. His destinations is 6 km along the beach from O. If he can row at 4km/h and walk at 5km/h towards what point on the beach should he row to reach his destination in the least possible time? Ans: 4km from O

Code:

o B
|\
| \
| \
| \
| \
o-----o---------o beach
O X D

B = boat

D = destination

OB = 3 km

OD = 8 km

Let OX = x km.

Time to reach X from B: .

Time to reach D from X:

Total time: , where x varies from 0 to 8.

Differentiate w.r.t. x, then solve . The answer should be x=4.