Mira rowed upstream in a stream flowing at the rate of 1.5 km/hr to a certain point and then rowed back stopping 2 kms short of the place where she originally started. If the rowing time was 2 hours 20 minutes and her uniform speed in still water was 4.5 km/hr, how far upstream did she go?
- 4.25 kms
- 5.33 kms
- 6.50 kms
- 7.00 kms
- 8.75 kms
The Usual Method
Speed of Mira in still water = 4.5 km/hr.
Speed of stream = 1.5 km/hr
Hence upstream travel speed = 4.5 – 1.5 = 3 km/hr
And downstream travel speed = 4.5 + 1.5 = 6 km/hr
Let the distance traveled upstream = x kms.
Time taken to travel upstream = hours
Time taken to travel downstream = hours
Total time taken = + = 2 hours 20 minutes
Estimated Time to arrive at the answer = 75 seconds.
Since the upstream travel speed = 4.5 – 1.5 = 3 km/hr and downstream travel speed = 4.5 + 1.5 = 6 km/hr (both being integers), but total travel time = hours (being a fraction with denominator as 3), the answer should also be a fraction with denominator as 3. The only answer satisfying this condition is 5.33 kms.
Estimated Time to arrive at the answer = 5 seconds.