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Question Video: Finding the Missing Number in a Sequence of Thousands Mathematics

Find the missing number in the following sequence. 1,000, 2,000, 3,000, _, 5,000.


Video Transcript

Find the missing number in the following sequence. 1,000, 2,000, 3,000, what, 5,000.

We’re given a sequence of five numbers, but one of them is missing. We need to find it. And to find the missing number in a sequence, we need to look at how the numbers change. So, let’s begin by looking at our first number. It’s the number 1,000. We write it using a one in the thousands place and then three zeros to show our empty hundreds, tens, and ones places.

The second number in our sequence is 2,000. And if we want to write 2,000 using this place value grid, we just need to change the one digit in the thousands place for the digit two. We’ve got one more 1,000. Do you think that our sequence might be to add 1,000 each time? It’s always important to look at the next number along too, because this could be a doubling sequence. Now, if we’re right and we need to add 1,000 each time, the next number after 2,000 won’t have a two in the thousands place. It’ll have one more than two; it’ll be three. And that’s exactly what we do have. In the sequence, we need to count in thousands. 1,000, 2,000, 3,000. And now if we add one more 1,000, we’re going to have 4,000. And we write the number 4,000 with a four in the thousands place followed by three zeros.

Now there’s one more thing we need to include, because the numbers in this sequence have a comma between the thousands and the hundreds digits. This is just a way of separating digits into groups to make numbers easier to read. All our thousands numbers in this sequence do have one of these commas, so we’re going to include it for 4000. Let’s read our sequence then, and we’ll model it using place value blocks as we say each number. 1,000, 2,000, 3,000, 4,000, 5,000. The missing number in our sequence of counting in thousands is 4,000.

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