How To Teach Algebra In Missing Number Problems

Hi, my name's Brooke, and in this video, we'll be looking at solving missing number problems using algebra. So let's take a look at our question. If 18A equals 27, what is a worth? So some people might find this a little bit daunting at first, but it's important to remind pupils that you can simply put a question mark in and it's the same. So 18 plus question mark equals 27. Now, a really useful way of working this out is using balancing scales. So If I put 18 plus A on this side and 27 on the other side, we can see that the scales are balanced. So I need to find out what the value of A is without affecting the balance of the scales. And to do this, I need to make sure what I do to one side, I also do to the other. I can't take away A yet because I'm not sure what it is, but I can take away 18 from each side. So on this side I would be left with a, and if I take away 18 from this side, I'd be left with nine. So I think that A is equal to nine. But at this point, I'd be expecting pupils to plug their answer back into the question. So 18 plus 9 equals 27 and that calculation is correct. So A is worth 9, and that's how you solve missing number problems using algebra.