You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: The ratio between the speeds of two trains is 7 : 8. If the second train runs 400 kms in 4 hours, then the speed of the first train is:

 Option A: 70 km/hr

 Option B: 75 km/hr

 Option C: 84 km/hr

 Option D: 87.5 km/hr

 Option E: 88.5 km/hr
[A]: Option D


[Q]: Question: A reduction of 25% in the price of oil enables a house wife to obtain 5kgs more for Rs.800, what is the reduced price for kg?

 Option A: 72

 Option B: 27

 Option C: 40

 Option D: 28

 Option E: 20
[A]: Option C


[Q]: Question: Four brothers Adam, Bill, Charles and David together contributed certain amount of money and purchased a car. The contribution made by Adam is half that of the total contribution made by the other three brothers, contribution made by Bill is one-fourth of the total contribution made by the other three brothers and the contribution made by Charles is two-third of the total contribution made by the other three brothers. If the total price of the car is $9750, find the contribution made by David.

 Option A: $540

 Option B: $580

 Option C: $600

 Option D: $650

 Option E: $680
[A]:
Option D