Question Video: Adding within 100 Including Finding the Missing Addend Mathematics

Video Transcript

Fill in the blank: the missing number plus 80 equals 100.

We can use a number line, counting in tens, to help us find the missing number. So we need to start at 80 and count forward in tens until we reach 100: 80, 90, 100. 20 plus 80 makes 100. The missing number is 20.