Multiple choice

Boat takes 7 hours to goes 105 km in upstream and it takes 4 hours to cove 90 km distance in downstream. what is the speed of boat in still water ?

  1. $37.5 km/ hr.$
  2. $28.75 km/ hr.$
  3. $13.75 km/ hr.$
  4. $18.75 km/ hr.$

  5. None of these.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Upstream: distance = 105 km, time = 7 hours, so upstream speed = 105/7 = 15 km/hr = b - s. Downstream: distance = 90 km, time = 4 hours, so downstream speed = 90/4 = 22.5 km/hr = b + s. Adding: 2b = 15 + 22.5 = 37.5, so b = 18.75 km/hr (boat speed in still water). Stream speed s = 22.5 - 18.75 = 3.75 km/hr. Option D is correct.

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