amy finished watching tv at 4:05, if she have been wqtching it for 2:15, what time was it when she started

2:10???

4:05 is equivalent to 3:65

3:65 - 2:15 = 1:50

think of it as a subtraction problem, where each column is 60's instead of 10's (because of 60 minutes in an hour)

4 05
-2 15

you can't subtract 15 from 5, so you borrow a 60 from the hour column:

3 65
- 2 15
--------
1 50

check:
2 hours from 2:15 is 4:15
but, 4:05 is ten minutes earlier than 4:15, so she watched for only 1:50

To find out what time it was when Amy started watching TV, you need to subtract the duration of her TV-watching (2 hours and 15 minutes) from the time she finished watching (4:05).

First, convert the 2 hours and 15 minutes into decimal form. There are 60 minutes in an hour, so divide 15 minutes by 60 to get 0.25 hours.

Thus, 2 hours and 15 minutes is equivalent to 2 + 0.25 = 2.25 hours.

Now, subtract 2.25 hours from the finishing time of 4:05.

4:05 - 2.25 hours = 1:40

Therefore, Amy started watching TV at 1:40.