Finding the unknown (add/sub)
Filling in the gaps
When we need to fill in the gaps, or find the missing number, there are quite a few ways we could do this. One of the best ways is to use things we already know! Some of the things that are really useful for finding missing numbers include:
- fact families
- bridge to 10
- using objects, and
- place value
Let's check out some problems, and see which methods can help us fill in the gaps with some addition problems. We might even find other methods, as well as those above.
What about subtraction?
The best part of this is that we can use the same strategies as we've used above, but we could also use number lines to help us. Watch Video 2 to see how we use number lines, fact families, and counting to $10$10, to work out the missing number.
There could even be other ways to find missing numbers, but the ones above are a great starting point.
Examples
Question 1
What must $x$x equal to make the following equation true?
$6+x=13$6+x=13
QUESTION 2
What must $j$j equal to make the following equation true?
$j-1=7$j−1=7
QUESTION 3
What must $p$p equal to make the following equation true?
$16+p=19$16+p=19