500
You have two pieces of string. One is 27 cm and the other is 45 cm. You want to cut smaller pieces of each in equal lengths. Each length needs to be a whole number. What lengths are possible for the 27 cm piece? The 45 piece? What's the greatest common length?
What is 9, 27, 3, 1. What is 15, 5, 1, 45, 9, 3. Greatest common length is 9.