instruction:
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:
Question: The average marks of a class of 35 students is 45 and that of another class of 55 students is 65. Find the average marks of all the students?

 Option A: 52.6

 Option B: 52.4

 Option C: 52.1

 Option D: 57

 Option E: 52.9
answer:
Option D


question:
Question: A die is rolled twice. What is the probability of getting a sum equal to 9?

 Option A: 2/3

 Option B: 2/9

 Option C: 1/3

 Option D: 1/9

 Option E: 1/10
answer:
Option D


question:
Question: A train covers a certain distance at a speed of 400kmph in 3 hours. To cover the same distance in 2 2/3 hours, it must travel at a speed of

 Option A: 480km/hr

 Option B: 450km/hr

 Option C: 550km/hr

 Option D: 750km/hr

 Option E: 650km/hr
answer:

Option B