Consider the question. Alex makes luxury dresses out of silk. Each dress needs 5 meters of silk and Alex has 600 meters of silk in storage. His friends also want to learn how to make these dresses so Alex gives all 5 of them 20 meters of silk each. He uses the rest to make dresses himself. How many dresses can Alex make?
 If the answer is '100'; explain the reasoning:
Alex gives his friends a total of 5 friends * 20 meters of silk = 100 meters of silk. This means he has 600 – 100 = 500 meters of silk left in storage. He can therefore make 500 meters of silk / 5 meters of silk per dress = 100 dresses.