A nine-floor apartment building has an average of four electrical circuits for each apartment. There are six apartments on each floor and one additional apartment on the roof. How many electrical circuits are in total?

• A. 200 circuits
• B. 220 circuits
• C. 240 circuits
• D. 260 circuits

Answer: (B)

Count all the apartments first. Six apartments on each of nine floors gives 9 × 6 = 54 apartments on the floors. The roof adds one more apartment, so there are 55 apartments in total. With four circuits per apartment, the total Circuits = 55 × 4 = 220. The roof apartment is just one more unit, adding four circuits like any other apartment.