A boat can travel with a speed of 5km/hr in still water. If the speed of the stream is 5km/hr, find the time taken by the boat to go 100km downstream.  Choose the correct choice from the following.
A) 1 hr
B) 2 hrs
C) 3 hrs
D) 4 hrs
E) 10 hrs

Rationale: "speed downstream = ( 5 + 5 ) km / hr = 10 km / hr . time taken to travel 100 km downstream = 100 / 10 hrs = 10 hrs . answer : e"
Answer: E