📖Definition
In these questions, you're presented with a sum that has a number missing. You need to find that missing number.
✏️Example
5 x 4 = 17 + ( ___ )
Knowledge Required
Know your Times Tables! Also, practise your mental arithmetic.
✅How To Answer
There are two main parts to answering this type of question.
First, work out the sums. If there's more than one operation, do them one at a time and ALWAYS work from left to right.
Then, once that's done, treat the problem as a simple equation.
And don't forget - the basic equation rule applies:
Whatever you do to one side of the equals sign, you must do to the other.
OK. The first thing to do is to work out the sums.
Looking at the left hand side:
5 x 4 = 20.
Now we can write: 20 = 17 + ( ___ )
This is our equation.
We want to get the missing value, ie. the ( ___ ) on its own.
As we said above, what we do to one side of the = we must do to the other.
Subtract 17 from both sides.
20 - 17 = ( ___ )
which becomes
3 = ( ___ )
Sometimes there will be more than one part to the sums on either side.
✏️Example
12 ÷ 4 + 7 = 3 x 5 - ( ___ )
As before, do it in stages and do one side at a time.
Starting with the left hand side, 12 ÷ 4 = 3 so we can write it:
3 + 7 which is 10.
Now look at the right hand side.
3 x 5 = 15
So, the whole thing becomes:
10 = 15 - ( ___ )
Subtract 10 from each side to get:
0 = 5 - ( ___ )
Add ( ___ ) to each side to get:
( ___ ) = 5.