City A to City B is a downstream journey on a stream which flows at a speed of 5km/hr. Boats P and Q run a shuttle service between the two cities that are 300 kms apart. Boat P, which starts from City A has a still-water speed of 25km/hr, while boat Q, which starts from city B at the same time has a still-water speed of 15km/hr. When will the two boats meet for the first time? (this part is easy) When and where will they meet for the second time?
A. 7.5 hours and 15 hours
B. 7.5 hours and 18 hours
C. 8 hours and 18 hours
D. 7.5 hours and 20 hours
E. 8.5 hours and 14 hours
Are You Up For the Challenge: 700 Level Questions
Spoiler: OA
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Nidzo
Jan 19 at 01:07am
P's Speed 1st Journey: 25 + 5 = 30 km/h
Q's Speed 1st Journey: 15 - 5 = 10 km/h
Time Boats Meet for the 1st Time:
As they are travelling towards one another their relative speed is 40 km/h.
hours.
Time Boats Meet for the 2nd Time:
It will take P 10 hours to complete the 1st 300km journey. After 10 hours Q will have covered 100km, and be 200km away from P. P's speed will change now to 20km/h as it will be going upstream, whereas Q will still be on its first journey and thus will maintain its speed of 10km/h.
As P and Q are travelling in the same direction now, their relative speed will be 10km/h, to cover 200km.
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Explanation:
City A to City B is a downstream journey on a stream which flows at a speed of 5km/hr. Boats P and Q run a shuttle service between the two cities that are 300 kms apart. Boat P, which starts from City A has a still-water speed of 25km/hr, while boat Q, which starts from city B at the same time has a still-water speed of 15km/hr. When will the two boats meet for the first time? (this part is easy) When and where will they meet for the second time?
A. 7.5 hours and 15 hours
B. 7.5 hours and 18 hours
C. 8 hours and 18 hours
D. 7.5 hours and 20 hours
E. 8.5 hours and 14 hours
Are You Up For the Challenge: 700 Level Questions
Spoiler: OA
Kudos
0 kudos, 1 bookmark
Nidzo
Jan 19 at 01:07am
P's Speed 1st Journey: 25 + 5 = 30 km/h
Q's Speed 1st Journey: 15 - 5 = 10 km/h
Time Boats Meet for the 1st Time:
As they are travelling towards one another their relative speed is 40 km/h.
hours.
Time Boats Meet for the 2nd Time:
It will take P 10 hours to complete the 1st 300km journey. After 10 hours Q will have covered 100km, and be 200km away from P. P's speed will change now to 20km/h as it will be going upstream, whereas Q will still be on its first journey and thus will maintain its speed of 10km/h.
As P and Q are travelling in the same direction now, their relative speed will be 10km/h, to cover 200km.
hours.
Answer D