Find the missing number.
We’re given a part–whole model. We’re not given the whole amount,
but we know the two parts, 300 and 400. We need to add these two parts
together to find the whole amount.
Here are three hundreds. Let’s add four more. 100, 200, 300, 400. How many hundreds are there
altogether? One, two, three, four, five, six,
seven. There are seven hundreds, no tens,
and no ones. 300 and 400 gives us a total of
700. The missing number is 700.