Question. Earl started delivering newspapers on the first floor of a condominium building. He then went up 5 floors then went down 2 floors. He again went up 7 floors and found that he is 9 floors away from the top of the building. How many floors does the building have?
Answer. 20
What step-by-step reasoning justifies that answer?
Reasoning: Earl was on the 1 + 5 = 6th floor after going up 5 floors. When he went down 2 floors, he was on the 6 - 2 = 4th floor. Since he went up 7 floors, he was then on the 4 + 7 = 11th floor. Since he is 9 floors away from the top of the building, therefore the building has 11 + 9 = 20 floors.