question: Hannah needs to drink 100 ml of water for every 200 calories she burns. She spends 2 hours doing aerobics, which burns 500 calories/hour, and 1 hour running, which burns 600 calories/hour. How many ml of water does she need to drink?
answer: First find the total calories burned on aerobics: 2 hours * 500 calories/hour = <<2*500=1000>>1000 calories
  Then add the calories burned running to find the total calories burned: 600 calories + 1000 calories = <<600+1000=1600>>1600 calories
  Finally, divide that number by the ratio of calories burned to water drunk to find how many water Hannah needs to drink: 1600 calories * 100 ml/200 calories = <<1600*100/200=800>>800 ml
  #### 800