40 plus 1000 equals the missing number.
The missing number is the sum of 40 and 1000. In other words, we need to add together 40 and 1000. One way we could do this is to use column addition. It’s important to remember to line the digits up in the correct column. This is the ones column. 1000 has no ones, and 40 has no ones. So zero plus zero equals zero.
Next, we move into the tens column. 1000 has no tens, and 40 has four tens. So we’re adding four tens. Zero plus four equals four. There’s nothing to add in the hundreds column. Zero plus nothing is zero.
Finally, we move into the thousands column. And there’s nothing to add here either. One plus nothing equals one. So 40 plus 1000 or 1000 plus 40 equals 1040.