After completing repairs on an elevator a maintenance engine

After completing repairs on an elevator, a maintenance engineer tested his work by sending the elevator up 12 floors, down 18 floors, and back up 20 floors. If the elevator ended up on the 30th floor, on which floor did the engineer begin his test?

Solution

Let X be the floor where the maintenance engineer tested his work \'

Then , at first he sent the elevator up 12 floors, so the elevator is now on the floor X + 12

Next he sent the elevator down 18 floors,so the elevator is now on the floor X + 12 - 18

And he sent the elevator back up 20 floors,so the elevator is now on the floor X + 12 - 18 + 20

But according to given problem, the elevator is now on the floor 30.

That is X + 12 - 18 + 20 = 30 implies that X = 16

That is on 16 th floor the engineer did begin his test