Question Video: Counting in Fifties to 1000 Mathematics

Count the objects. Michael made trays of 5 cookies. Count in 5s to find how many cookies he made. Madison bought boxes of 50 cookies. Count in 50s to find how many cookies she bought.

04:10

Video Transcript

Count the objects. Michael made trays of five cookies. Count in fives to find how many cookies he made. Madison bought boxes of 50 cookies. Count in 50s to find how many cookies she bought.

Rather than saying every single number, there’re often quicker ways to count. And this question gets us counting in fives. We do this in the first part of the question. And also counting in 50s, we do this in the second part of the question. Now, if we know how to count in fives, we can use this to help us count in 50s. So let’s look at the first part of the problem. We’re told that Michael made trays of five cookies. And if we look at each tray, we can see that they all have five cookies on them. The question tells us to find how many cookies he made. So we need to count the number of cookies there are all together.

One way to do this will be to count every single cookie, one, two, three, and so on. But because Michael has made trays of five cookies, we could skip count in fives to find the total. We can see that the first two numbers have been filled in, five, 10. Let’s continue to skip count in fives, 15, 20, 25. We skip counted in fives to find the total. And if we look at the numbers that we said as we skip counted in fives, we can see a pattern. They end in the digits five, then zero, then five again, then zero, and so on. Five, 10, 15, 20, 25. And so the number of cookies that Michael made is 25.

In the second part of the problem, we have some more objects to count. This time, we’re told about Madison who has bought boxes of 50 cookies. At this time, even if we wanted to count every single cookie, we can’t. We can’t see them. This is a good job because we’re not being asked to count every single cookie. We have to count in 50s. What do we know about the number 50? 50 is 10 lots of five. So if we know how to count in fives, we can use this to help us count in 50s. The answers will be 10 times as large.

We can see this by looking at the first two numbers that have already been completed. Instead of five, we have a number that’s 10 times as large as five, 50. And instead of 10, we have a number that’s 10 times as large as 10, 100. Because these numbers are 10 times as large, the digits have shifted one place to the left. So this has the effect of looking like we’ve added a zero onto all the numbers that we had when we counted in fives. Let’s start with 100 then and carry on skip counting in 50s, 150, 200, 250. The number of cookies that Madison bought is 250. Look at this number. It’s 10 times as large as the number of cookies that Michael made.

Both children had five groups of cookies. Michael had five trays. And Madison had five boxes. But each of them had a different number of cookies in each group. Michael had five groups of five. So we counted in fives to find the answer. Five groups of five is 25. But Madison had 10 times as many cookies in each group. She had five groups of 50. So we needed to count in 50s to find the number of cookies that she bought. Five lots of 50 equals 250.

The answers are 25 and 250.

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