conversations.from: human
conversations.value: Twice Betty's age is the cost of a pack of nuts. Doug, Betty's friend, is 40 years old. If the sum of their ages is 90, and Betty wants to buy 20 packs of the nuts, calculate the amount of money she'll pay for the packs of nuts.
  How to solve this?
conversations.from: assistant
conversations.value: If Doug, Betty's friend, is 40 years old, and the sum of their ages is 90, Betty is 90-40 = 50 years old.
  Since twice Betty's age is the cost of a pack of nuts, a pack of nuts is sold at 2*$50 = $100
  If Betty wants to buy 20 packs of the nuts, she'll have to pay 20*$100 = $2000