question: Johnny took his allowance of $20 and added an extra $10 to it.  He then invested this sum of money, which tripled in a year.  How much money did he have after a year?
answer: Johnny invested twenty and ten dollars for a total of 20+10=<<20+10=30>>30 dollars invested
  Johnny tripled this amount of money over the year, for a total of 30*=90 dollars
  #### 90