There are 3 cups of water wasted every 24hrs.

How much is wasted in 1 week.

First we know that there are 24hrs in every day and 7 days in every week.

So there are 3 cups of water wasted every day(every 24hrs).

To find out how many cups of water are wasted in a week you would do: 3 cups * 7 days since there are 7 days in a week

3*7 = 21 cups of water wasted in a week.

PROBLEM: 3 cups water wasted in 24 hours (1 day)

FIND: How many cups are wasted in a week (7 days)?

SOLUTION 1: You can add 3 for each day of the week so 3+3+3+3+3+3+3 = 21 Cups

SOLUTION 2: Since we are using the same number for each day, we can multiply 3*7 = 21 Cups

Either solution will get you the answer you need but the purpose of this question if to go with Solution 2 which would be faster when the problem becomes more complex.

24 hours mean 1 day.

In 1 day, cups of water wasted = 3. (This is given in your question)

Therefore in 1*7 days, cups of water wasted = 3*7 = 21

Now 7 days mean 1 week.

Therefore, in 1 week 21 cups of water are wasted.