Video Transcript
Find the missing number. Nine plus seven equals what plus
nine.
You know we can find the answer to
this question without doing any adding at all. But to do this, we need to look
very carefully at what the question tells us. We’re given two additions here with
an equal sign in between. This shows that they’re worth the
same. Nine plus seven is the same as
something add nine. Now, if we look at these two
additions, we can see something very similar. They both contain the number
nine. Now, in the first addition, the
number that’s added to nine is seven. In the second addition, nine is
added on to a number. But we don’t know what that number
is. And so nine and seven make exactly
the same number as nine and seven. This is the only answer that makes
sense. The additions are the same. It’s just the numbers have been
swapped around. And we know that if we add two
numbers in a different order, they make the same total.
If you have time, try working out
the answer in the two different ways. But we don’t need to actually do
this to answer the question. Nine plus seven gives exactly the
same answer as seven plus nine. The missing number is seven.
