Jacob is excited to show his toy train to his friends. The engine runs on a battery and can pull cars. He has built a track for the train. The track makes turns and goes through a tunnel. It also has a hill. Jacob has 10 cars for his train. When they are all used, the train cannot make it up the hill. Explain what Jacob could do to answer this question: How many cars can the train pull up the hill?

In order to answer the question of the number of cars Jacob's train can pull up the hill, he would need to use a trial and error method by decreasing the number of cars loaded on the train one after the other and pulling the train up the hill in each case.

Since using all the 10 cars prevents the train from making it up the hill, the next thing to do would be to decrease the number of cars on the train to 9 by removing 1 and then trying to pull the train up the hill again. If it still would not move up the hill, next would be to decrease the number of cars to 8, 7, 6, etc. until it gets to the number of cars the train can successfully pull up the hill.

This would effectively answer the question of how many cars can the train pull up the hill.