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? A.85 km/hr B. 87.5

Question

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?

 

A. 85 km/hr

 

B. 87.5 km/hr

 

C. 90 km/hr

 

D. 92.5 km/hr

Answer 1

First, 400k in 4h is 100kph

 

Second, this question is a proportion, which can be stated in the following way:

7 is to 8 as 100kph is to x, or 7/8 = x/100kph

 

700kph = 8x; divide both sides by 8, which gives x = 87.5kph

 

So, the answer is option B

Answer 2

The speed of the second train is 400 (km)/(4 hours) = 100 km/hr.  To find the speed of the first train, set up a proportion:

 

7/8 = x/100

 

Solve for x.