The tree diagram shows that there are a total of six sample spaces.
  math------science
  art
  
  science---math
  
  art---math
  science
  
  math---art
  
  art---science
  math
  
  science---art
  
  Based on the tree diagram, the probability that the science project is first is two over six. This is because science appears first in two out of the six sample spaces (boldened).