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.

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
Option D

Question: When n is divided by 19, the remainder is 7. When n is divided by 11, the quotient is equal to Z, and the remainder is equal to 7. Z must be divisible by which of the following numbers?

 Option A: 16

 Option B: 18

 Option C: 20

 Option D: 19

 Option E: 22
Option D

Question: The average of 45 results is 25 and the average of other 25 results is 45 . what is the average of all the results?

 Option A: 24

 Option B: 32

 Option C: 48

 Option D: 50

 Option E: None

Option B