conversations.from: human
conversations.value: Marky owns a computer accessory shop. For this month, half of their sales are wireless mice, one-fourth are optical mice, and the rest are trackball mice. If Marky's shop was able to sell a total of 80 mice, how many of them are trackball mice?
conversations.from: assistant
conversations.value: There were 80/2 = 40 wireless mice sold.
  There were 80/4 = 20 optical mice sold.
  So, there were a total of 40 + 20 = 60 wireless and optical mice sold.
  Therefore, 80 - 60 = 20 trackball mice were sold this month.