Here we have 4 worksheets on adding three numbers to make 20. On the first page, one of the numbers is always 10, making it very similar to adding two numbers to make 10. The third and fourth pages only have one number given so that there are a range of possible answers. Don't forget that zero could be an option on these addition pages.
This activity could be extended into a mini investigation on how many different ways can you make 20 using three whole numbers.
Add 3 numbers to make 20