Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.
--------
Question: Problem: a trader mixes 80 kg of tea at 15 per kg with 20 kg of tea at cost price of 20 per kg. in order to earn a profit of 25 %, what should be the sale price of the mixed tea ?
Options: a. 23.75, b. 22, c. 20, d. 19.20, e. none of these

Answer: c


Question: Problem: how much is 60 % of 40 is greater than 4 / 5 of 30 ?
Options: a. 8, b. 3, c. 7, d. 0, e. 1

Answer: d


Question: Problem: the rate of spin of a certain gyroscope doubled every 15 seconds from the moment a particular stopwatch started. if after a minute and a half the gyroscope reached a speed of 400 meters per second, what was the speed, in meters per second, when the stopwatch was started ?
Options: a. 25 / 2, b. 25 / 4, c. 25 / 8, d. 25 / 16, e. 25 / 32

Answer:
b