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KCC's quiz AQQ274 about 2 sportsmen running and walking

Two  sportsmen A and B have exactly the same running speed and the same walking speed.

One day they started the same trip to the same place.

Sportsman-A walked for half of the distance and ran for the rest, while

Sportsman-B walked for half the time and ran for the other half of time.

Question: Which sportsman reached the end of the trip first? How do you justify it?

Good luck and try to be among the firsts!

P.S. Pass those quizzes among your colleagues and friends; we all need such small brainstorming time to time!

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Parents
  • Let R equal running speed and W equal walking speed.

    Time for A to travel distance D:  D/2W+D/2R = (D/2)[1/W+1/R] = D(W+R)/2WR

    Time for B to travel distance D:  2D/(W+R)

    Let W=kR where 0< k <1:  Walking speed less than running speed

    Ta/Tb = [(W+R)^2]/4WR = [(k+1)^2]/4k

    If Ta/Tb < 1 then k^2+2k+1<4k or (k-1)^2<0 :FALSE

    If Ta/Tb > 1 then k^2+2k+1>4k or (k-1)^2>0 :TRUE

    Therefore, Tb is less then Ta and sportsman B finishes first.

Reply
  • Let R equal running speed and W equal walking speed.

    Time for A to travel distance D:  D/2W+D/2R = (D/2)[1/W+1/R] = D(W+R)/2WR

    Time for B to travel distance D:  2D/(W+R)

    Let W=kR where 0< k <1:  Walking speed less than running speed

    Ta/Tb = [(W+R)^2]/4WR = [(k+1)^2]/4k

    If Ta/Tb < 1 then k^2+2k+1<4k or (k-1)^2<0 :FALSE

    If Ta/Tb > 1 then k^2+2k+1>4k or (k-1)^2>0 :TRUE

    Therefore, Tb is less then Ta and sportsman B finishes first.

Children