# Marco picked up 9 rocks. He picked up 2 of them on his way to school. He picked up the rest on his way home. How many rocks did Marco pick up on his way home?

If Marcus picked up 9 rocks, and 2 were on his way to school, that means that the rest were left for the way home. So, you can use the equation $9 - 2$ to figure out how many were picked up while walking home. Since $9 - 2 = 7$, you know that $7$ rocks were picked up on the way home.