TASK DEFINITION: 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.
PROBLEM: Question: A man rows his boat 85 km downstream and 45 km upstream, taking 2 1/2 hours each time. Find the speed of the stream?

 Option A: 6 kmph

 Option B: 9 kmph

 Option C: 3 kmph

 Option D: 8 kmph

 Option E: 1 kmph

SOLUTION: Option D

PROBLEM: Question: One-tenth of the students at a nursery school are 4 years old or older. If 20 students have not yet reached their third birthday, and a total of 50 students are not between 3 years old and 4 years old, how many children are in the nursery school?

 Option A: 150

 Option B: 300

 Option C: 450

 Option D: 490

 Option E: 620

SOLUTION: Option B

PROBLEM: Question: A, B and C enter into partnership. A invests some money at the beginning, B invests double the amount after 6 months, and C invests thrice the amount after 8 months. If the annual gain be Rs.18900. A's share is?

 Option A: 6300

 Option B: 2765

 Option C: 6000

 Option D: 1298

 Option E: 1261

SOLUTION:
Option A