The United States generates and uses about 71 quads of energ
     The United States generates and uses about 71 quads of energy each year and its renewable sources generate about 40 GW. If the renewable sources are generating power about a third of the time, what fraction of its energy usage is based on renewable sources? 
  
  Solution
E= total energy generating in a year= 71 quads
R= renewable energy= 3*40 GW
Fraction= 3*40/71 (Gw/quards)

