Answer: Cole and his sister Chloe will take 81 minutes to clean the whole house.
Explanation:
Total rooms in the house = 9
Total persons to clean the house = 2 (Cole and his sister Chloe)
Time taken by 1 person to clean one=18 minutes
Time taken by 2 persons to clean one room together=18 divided by 2 = 9 minutes
Time taken by 2 persons to clean 9 rooms (which is the total number of rooms in the house)=9 multiply 9 = 81 minutes
therefore, they will take 81 minutes to clean the whole house.