The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, What is the the speed of the first train?  Pick one
A) 87.0
B) 87.5
C) 87.2
D) 87.1
E) 87.4
Speed and time are inversely proportional (when distance is constant) ⇒Speed ∝ 1Time (when distance is constant)   Here distance is constant and hence speed and time are inversely proportionalSpeed ∝ 1Time⇒Speed1Speed2=Time2Time1⇒78=4Time1⇒Time1 = 4×87 hr⇒Speed of the first train = DistanceTime1=400(4×87)=100×78=12.5×7=87.5 km/hr   Answer :87.5
<result>B</result>
The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 km in 4 hours, What is the the speed of the first train?