Question Video: Multiplying 5-Digit Numbers by 1-Digit Numbers

Video Transcript

Calculate the following. 27894 multiplied by three.

In this question, we have a five-digit number. In this question, we have a five-digit number. This contains four ones, nine 10s, eight 100s, seven 1000s, and two 10s of 1000s. And we’re multiplying this number, which is 27894, by a single digit, three. And the calculation has been set out vertically like this for one reason. It’s so that we can use a type of written multiplication that helps us multiply each digit separately. We call this short multiplication because we’re only multiplying by a single digit.

We can multiply each digit in turn. Let’s start off by looking at the ones. What are four ones multiplied by three? Well, we know four times three equals 12. So, the answer’s going to be 12 ones. 12 ones are the same as two ones and one 10.

Now, we can multiply the tens digit, which is nine. What is nine times three? We know that 10 times three is 30, so nine times three must be three less than 30. The answer is 27. Nine 10s times three is 27 10s. We already have one 10 underneath, so that’s 28 10s. We need to write 28. We’re gonna write the eight in the tens place and write our 20 10s as two 100s.

Onto the hundreds digit. If we know that nine threes are 27, then eight threes must be another three less than 27. Eight threes are 24. So, eight 100s multiplied by three is 24 100s. We already have two 100s underneath. That takes us to 26 100s, which is the same as 2600.

And if we look at our thousands digit, it’s gone down again. We said that eight threes were 24, so seven threes must be three less than 24. That’s 21. So, we can say seven 1000s multiplied by three are 21 1000s. We already have two 1000s underneath. That takes us to 23 1000s. And we write the three in the thousands place and our two, which represents 20 1000s, in the ten thousands place. Finally, two times three is six. So, two lots of 10000 times three are six lots of 10000. Plus the two underneath takes us to eight lots of 10000.

The final thing we can do is to write our answer, using a comma to separate the thousands from the hundreds digits. This just makes it easier to read. This calculation was already written for us vertically, so we knew which method we were supposed to use. 27894 multiplied by three equals 83682.