conversations.from: human
conversations.value: Shawn collected 40 plain pebbles. He painted 9 pebbles red and 13 pebbles blue. He then divided the remaining pebbles equally into 3 groups, and painted them purple, yellow, and green. What is the difference between the number of blue and yellow pebbles?
  What is the solution?
conversations.from: assistant
conversations.value: After painting the red and blue pebbles, Shawn had a remainder of 40 - 9 - 13 = 18 pebbles.
  He painted 18/3 = 6 pebbles yellow.
  The difference between the number of blue and yellow pebbles is 13 - 6 = 7.