conversations.from: human
conversations.value: John puts $25 in his piggy bank every month for 2 years to save up for a vacation. He had to spend $400 from his piggy bank savings last week to repair his car. How many dollars are left in his piggy bank?
  Can you solve this problem?
conversations.from: assistant
conversations.value: He saved money for 2 years, which is equal to 12 x 2 = 24 months.
  The amount of money he saved is $25*24 = $600.
  But he spent some money so there is $600 - $400 = 200 left.