Video Transcript
Find the missing divisor. 90 divided by what equals 10.
Now, a divisor is the number that we divide by in a division calculation. And in this division calculation, we’re dividing 90 by something. And we need to find what this missing number is. We can use this bar model to help us understand what the question’s asking us. Let’s label the whole bar as being worth 90; this is the amount that we’re dividing.
And then, we can divide 90 into groups of a certain amount. We’re not sure what this missing divisor is, but what we do know is that if we divide 90 into groups of this amount, there will be 10 equal groups. So, in other words, 10 lots of our missing number will equal 90. We can actually write this as a number sentence. 10 lots of our missing number will equal 90. 10 times what equals 90? What we’ve done here is start with the answer and work backwards through the division.
And by looking at the inverse like this, we can use the inverse operation, which is multiplication. How many 10s are there in 90? Well, we know that if we were to make 90 out of place value counters, we’d have nine 10s and zero ones. So, we can say that 10 times nine is 90. So, each of the sections in our bar model must be worth nine.
We’ve found the missing divisor by reading the calculation backwards and using the inverse operation multiplication to help us. 10 times nine equals 90. And so, we know that 90 divided by nine must be equal to 10. The missing number, the divisor, in our calculation is nine.
