How To Teach Long Multiplication Of Two Digit By Two Digit Numbers

Hi, my name's Ben. We're going to be looking at the formal written method for long multiplication, or tens and ones times tens and ones. Now, this calculation will be calculated vertically and the children really have to understand that, which they will do if they've had a go at short multiplication. First, it's important that they look at the numbers as being partitioned. So 26 multiplied by 5 and 26 multiplied by 40, then we can proceed. You'll notice that I've done the 4 as in 40 in a different colour. I'll show you the why later. So 6 times 5 is 30. So we put a 0 in the ones column and we carry that 3 over into the tens. Then we look at 2 times 5. The children have to know that that's 2 tens times 5, which is 10 tens, plus the 3 tens makes 13 tension, which is 130. 26 times 5 equals 130. We then move on to 26 times 40. And that's why it's in a different color, because that's really useful and it's a good tip for children, so they can see the difference between the units and the tens. We have to factor in a zero because we are dealing with times in by 40 this time. So now we look at six times four, which is 24, which is actually 24 tens. So I'll write the four in the tens column and I'm going to carry that two over into the hundreds. We're then looking at two times four, which is eight. Again, it's two tens times four tens, which is 800. Plus these two hundreds here makes ten hundreds or 1000. The final stage, because we partitioned, is to recombine the two numbers. So 0 plus 0 is 0. 3 tens plus 4 tens is 7 tens, 100 plus zero hundred is 100, and 1000 on its own is 1000. So giving you the answer, 26 multiplied by 45 is 1170. And that's how you teach the formal written method for long multiplication.