Question Video: Multiplying Two-Digit Numbers by One-Digit Numbers | Nagwa Question Video: Multiplying Two-Digit Numbers by One-Digit Numbers | Nagwa

# Question Video: Multiplying Two-Digit Numbers by One-Digit Numbers Mathematics • Third Year of Primary School

Find the value of 90 × 3.

02:54

### Video Transcript

Find the value of 90 multiplied by three.

In this question, we’re being asked to multiply a multiple of 10 by a one-digit number. We know 90 is a multiple of 10 because it ends in a zero. That’s always a good way to spot them. And multiples of 10 are what we get when we multiply a number by 10. And 90 is nine 10s, isn’t it? This is a fact that we can use to help us find out the answer. And we can use place value blocks to help see how. So firstly, if we think of 90 as nine 10s, we can write our calculation as nine 10s multiplied by three, or in other words three lots of nine 10s.

Let’s model these using place value blocks. One, two, three lots of nine 10s. How many 10s blocks have we got here? Let’s use our knowledge of the three times table to help. Here we’ve got three lots of nine ones. And if we know how many ones blocks we’ve got, we also know how many 10s blocks we’ve got. Let’s count in nines three times. Nine, 18, 27. We’ve got 27 ones blocks. And because we’ve got nine 10s multiplied by three, we’ve also got 27 10s blocks.

But they’re not worth 27, are they? Remember, each of our 10s blocks is worth 10. And so to solve this problem, we need to take our answer to nine times three and multiply it by 10. The diagram on the right is 10 times as large as the one on the left because each of the blocks we’ve used is worth 10 times as much. So what’s 27 multiplied by 10? Well, we know when we multiply any number by 10, each of its digits becomes 10 times as large. And so it shifts one place to the left. Instead of the two in 27 being worth two 10s, it shifts one place to the left and is now worth two 100s. Instead of the seven in 27 being worth seven ones, that also shifts one place to the left and is now worth seven 10s. And we need to include a zero to show that we’ve got an empty ones column. 27 multiplied by 10 equals 270.

We’ve found the answer to 90 multiplied by three by thinking of the calculation as nine 10s multiplied by three. We know that nine 10s are 10 times as large as nine ones. So first, we found the answer to nine ones multiplied by three, which was a lot easier. Nine times three equals 27. And then we just found the number that was 10 times as large as this by multiplying 27 by 10. The value of 90 times three equals 270.

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