The battery charge in Mary’s cordless vacuum cleaner lasts ten minutes. It takes her four minutes to vacuum each room in her house. Mary has three bedrooms, a kitchen, and a living room. How many times does Mary need to charge her vacuum cleaner to vacuum her whole house? Let's be accurate as possible.
Mary has 3 + 1 + 1 = 5 rooms in her house. At 4 minutes a room, it will take her 4 * 5 = 20 minutes to vacuum her whole house. At 10 minutes a charge, she will need to charge her vacuum cleaner 20 / 10 = 2 times to vacuum her whole house.
The answer: 2.