Answer: 108 rooms
Step-by-step explanation: To solve this problem, we can set up a proportion. In the numerator of our first fraction, we will have the number of rooms Robin can clean and in the denominator, we have the time it takes him to clean 72 rooms which is 6 days.
In our second fraction, we don’t know how many rooms he can clean in 9 days. In fact, that’s what the problem is asking. Since we don’t know how many rooms Robin can clean in 9 days, we can put a variable in the numerator is our fraction. A variable is a letter that represents any number. I will use the variable “x” in this problem. In the position of the denominator, we have the time it takes him to clean X rooms which is 9 days.
Solving from here, we can use cross products so we multiply diagonally.
We have 72 rooms over 6 days equals X rooms over 9 days or 648 = 6x.
Solving from here, divide both sides by 6 and we find that x is equal to 108 which means that Robin can clean 108 rooms in 9 days.
