Video: Finding Missing Numbers When Multiplying by 100

Fill in the blanks: 30 × 30 = _ × 100 = _.


Video Transcript

Fill in the blanks. 30 multiplied by 30 equals what multiplied by 100 equals what.

There are three parts to this number sentence. And they’re all worth the same. 30 times 30 is exactly the same as our missing number multiplied by 100 and is also exactly the same as a missing number or a value on the end. Can you see what we need to do to find the missing numbers? Well, only the full piece of information that we’ve been given is that each part of the number sentence equals 30 times 30. So let’s start by working out what is 30 times 30 worth.

Notice that both the numbers in this multiplication are multiples of 10. This means that we can use number facts we already know to help us. And we can multiply the answer by 10. The fact that we can use to help us is three times three. We know that three times three equals nine. So three times 30 will be 90. We’ve increased one of our number threes by 10 times as how our answer has increased by 10 times two. And finally, if we know that three times 30 is 90, then 30 times 30 will be 10 times as large as 90 which is 900.

So the value of 30 times 30, and in fact the value of all the expressions in this number line, is 900. So in actual fact, we’ve found our final missing number first. All of the expressions must be worth 900. So what’s our first missing number? What do we multiply by 100 to give 900? The answer is nine. Nine times 100 equals 900. We filled in the blanks by first finding out what 30 times 30 was worth and then using this to help. 30 times 30 equals nine times 100 equals 900. Our two missing numbers are nine and 900.

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