Video: Subtracting Integers Representing Dates

In the same year, how many days are there from the start of October 4th to the end of October 29th?

03:43

Video Transcript

In the same year, how many days are there from the start of October the fourth to the end of October the 29th?

This is very similar to our find-the-difference type of question. We need to work out how much time goes by between October the fourth and October the 29th. The tricky thing about questions like this is that sometimes it’s not clear whether we’re supposed to count the two days either end of the time that we’re thinking about. But thankfully in this question, it’s very clear. We need to start measuring from the start of October the fourth, so we do include October the fourth, till the end of October the 29th. So again we do include October the 29th.

We’d normally want to use a calendar to help us to work out a period of time like this. But we don’t have a calendar to look at. There’s nothing stopping us drawing one. We’ve drawn a grid with seven squares in each row. This represents the number of days in a week. So let’s start by labelling the days from the fourth to the 29th. Now, we could write the number four anywhere really on the grid. But it does make sense to write it at the start of a week. This way, we can practice counting in sevens which is a good skill when we’re working out dates using a calendar.

There’s our first week. And we can continue to complete the calendar row by row until we reach October the 29th. So we need to count the number of days from this point here which is the start of October the fourth to this point here which is the end of October the 29th. There are 31 days in October. We won’t need the last two days. But let’s complete them anyway just so that the calendar looks correct. And we’ll put in the first three days too.

First, we can ask ourselves, how many full weeks are there between the fourth and the 29th? One, two, three. There’s some more days on the end. But they don’t make a full week. Three weeks is the same as three multiplied by seven days. Three sevens are 21. So we know there are 21 days between the fourth and the 24th of October. Now, let’s add our extra days. One, two, three, four, five. We need to add five days to our total of 21 days. 21 plus five equals 26. There are 26 days from the start of October the fourth to the end of October the 29th.

Another way to find the answer could be to use a number line and to count on from four to 29. We need to be careful with this method as we’ve said already because this method doesn’t include the number we’d start with. To begin with, we could make a jump of 20. Four plus 20 takes us to 24. Then all we need to do is add another five to take us to 29. That’s a jump of 25 in total. But as we’ve said already, we need to include the number four because we’re talking about a day of the month. So we need to add one to our total. The number of days between the fourth and the 29th, if we include the fourth and the 29th, is 26 days.

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