# Video: Determining the Time after a Known Period

If Anthony started his homework at 5:20 am and it took him 50 minutes to complete it, when did he finish?

02:21

### Video Transcript

If Max started his homework at 5:20 am and it took him 50 minutes to complete it, when did he finish?

Max began doing his homework at 5:20 am. 5:20 Looks like this on a clock face. We’re told that it took Max 50 minutes to complete his homework. And we need to calculate the time that he finished. 50 minutes is going to take us into the next hour, past six o’clock. So, we can find the answer by counting to six o’clock and then adding on the rest of the minutes that we have left. So, in effect, what we’re doing is partitioning 50.

The first thing we can do is to count on until we get to six o’clock. We know there are 60 minutes in an hour. And so, if we’re already at the time of 5:20, we only have to add another 40 minutes to get to six o’clock. To prove this is true, we can count in fives around the clock face, five, 10, 15, 20, 25, 30, 35, 40. 40 minutes will take Max to six o’clock.

So, the first part of 50 that we’ve added is 40. What’s the second part? We’ve got another 10 minutes to add to make 50 minutes. If we start at 6 am and add 10 minutes, the time becomes 6:10 am. Again, we can count in fives on the clock face, five, 10.

We found the answer by counting on 40 minutes and then 10 minutes. The reason we did this is because 40 minutes took us to six o’clock am. We could then add the remainder very quickly. Six o’clock plus 10 minutes is 10 past six. If Max started his homework at 5:20 am, and it took him 50 minutes to complete it, he finished at 6:10 am.

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