UPSC CDS Math Speed, Time and Distance Questions

Speed of B=VB=

100

10

=10m/s
Let the time taken by A to finish the race be t seconds and the speed of A be vA m/s.
Distance covered by A in t seconds =1000m=vA×t
Distance covered by B in t seconds =900m=vB×t
∴

VA

VB

=

1000

900

⇒VA=

1000

900

×10=

100

9

m/s
Time taken by A to finish the race in the 2nd case =

100

100 9

=90 seconds
Time taken by B to finish the race in the 2nd caseTherefore, time by which A beat B =155−90=65 seconds