There were 20 balloons. Seven balloons flew away. How many balloons are left?
We’re told that there were 20
balloons. This is the number that we begin
with. But we’re then told that seven
balloons flew away. And we’re asked to calculate the
number of balloons that are left. In other words, what number is
seven less than 20? We need to work out 20 take away
seven to find the answer. One way we can find the answer is
to think of the number 20 as being worth two 10s. If we take away seven, one of those
10s is going to be broken up.
We can show this using ten
frames. Here are our two 10s. Now, if we take away seven from
these two 10s, one of our 10s, as we’ve said, is going to be broken up. So if we subtract seven from this
10, what are we going to be left with. We’re going to be left with the
number that pairs with seven to make 10. Seven plus three makes 10. So we’re left with one 10 and 3
ones. 20 take away seven equals 13. There’re 13 balloons left.
Let’s check that our answer is
correct by seeing whether 13 and seven make 20. We can start with 13 and then add
one, two, three, four, five, six, seven. The difference between 13 and 20 is
seven. And so 20 take away seven equals
13. There were 20 balloons. Seven balloons flew away. And now, there are 13 balloons