TSD Q2

.  A road network (shown in the figure below) connects cities A, B, C and D. All road segments are straight lines. Dis the mid-point on the road connecting A and C. Roads AB and BC are at right angles to each other with BC shorter than AB. The segment AB is 100 km long. Ms X and Mr Y leave A at 8.00 a.m., take different routes to city C and reach at the same time. X takes the highway from A to B to C and travels at an average speed of 61.875 kmph. Y takes the direct route AC and travels at 45 kmph on segment AD. Y's speed on segment DC is 55 kmph.

 

  Q. What is the average speed of Y?

  a) 47.5 kmph

  b) 49.5 kmph

  c) 50 kmph

  d) 52 kmph  

Y takes the direct route AC and travels at 45 km per hour on segment AD. Y's speed on segment DC is 55 km per hour.

AD=DC=a(D is the midpoint on the road connecting A and C.)

The time taken by Y to reach D= a/45

Further, the time taken by Y to reach C= a/55

Y has travelled equal distances are constant speed.

=> Average speed =  2*45*55/ 100 = 49.5 kmph

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