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 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?