In a 100m, A beats B by 15m and B beats C by 10m. If A beats C by 5 se

Responding to a pm:

In the same time, A covers 100m and B covers 85 m.
SpeedA : SpeedB = 100:85 = 20:17

In the same time, B covers 100m and C covers 90m.
SpeedB : SpeedC = 100:90 = 10:9

SpeedA : SpeedB : SpeedC = 200:170:153
A covers 200m in the time that C covers 153 m so in a 100 m race, when A finishes, C would have covered 76.5 m. Since A beats C by 5 secs, C covers the leftover 23.5 m in 5 secs.
Speed of C = 23.5/5 = 4.7 m/s

Answer (C)

We have 2 different time periods that are being talked about.

(1st) A finishes the race and beats B by 85 m

They both run for the same travel time, so distance covered over that time is directly proportional to speed

Dist of A : Dist of B = 100 : 85

(2nd) then B finished the race and beats C by 10 m

Dist of B : Dist of C = 100 : 90

When B covers 100 —————-> C can cover 90

When B covers 1 ————-> C can cover 90/100 = 9/10

When B covers 85 ———> C can cover (9/10) * 85 = 76.5


Thus, during the 1st time period when A finished the race

A ran 100 m
B ran 85 m
C ran 76.5 m


We are told that A beat C by 5 seconds (measured by the speed of C)

In terms of Distance, A beat C by 100 - 76.5 = 23.5 m


Speed of C = Dist / Time = (23.5) / (5) = 4.7 meters per second

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