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: Look at this series: 15, 15, 27, 27, 39, 39, 51, 51, 63, 63, ? ... What number should fill the blank?

 Option A: 51

 Option B: 39

 Option C: 75

 Option D: 15

 Option E: None
answer:
Option C


question:
Question: The average age of 3 boys is 15 years and their ages are in the proportion 1:2:3. The age of the youngest boy is?

 Option A: 10 years

 Option B: 12 years

 Option C: 15 years

 Option D: 18 years

 Option E: 7.5 years
answer:
Option E


question:
Question: An author received $0.80 in royalties for each of the first 100,000 copies of her book sold, and $0.90 in royalties for each additional copy sold. If she received a total of $260,000 in royalties, how many copies of her book were sold?

 Option A: 130,000

 Option B: 300,000

 Option C: 380,000

 Option D: 400,000

 Option E: 420,000
answer:

Option B