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: A car dealership has 40 cars on the lot, 30% of which are silver. If the dealership receives a new shipment of 80 cars, 40% of which are not silver, what percentage of total number of cars are silver?

 Option A: 35%

 Option B: 37.5%

 Option C: 45%

 Option D: 47.5%

 Option E: 50%

A: Option E
****
Q: Question: A train covers a distance of 12 km in 10 min. If it takes 10 sec to pass a telegraph post, then the length of the train is?

 Option A: 100

 Option B: 110

 Option C: 200

 Option D: 130

 Option E: 140

A: Option C
****
Q: Question: What will be the ratio of simple interest earned by certain amount at the same rate of interest for 4 years and that for 9 years?

 Option A: 1 : 3

 Option B: 2 : 3

 Option C: 1 : 2

 Option D: 4 : 9

 Option E: 1 : 4

A:
Option D
****