Dot problems with plus
You learn to find the missing number under the dot in an addition.
How to work it out
- Look at the answer and the known number.
- Take the known number away from the answer.
- Then you find exactly the number under the dot.
A worked example
24 + · = 60
- Look at the answer: 60.
- Take away the number you know, 24: 60 − 24 = 36.
- Check with an addition: 24 + 36 = 60.
- The number under the dot is 36.
More examples
35 + · = 60
- Take 35 away from 60.
- Work it out: 60 − 35 = 25.
- The number under the dot is 25.
· + 18 = 42
- Take 18 away from 42.
- Work it out: 42 − 18 = 24.
- The number under the dot is 24.
Try it yourself
· + 35 = 90
140 + · = 200
Watch out
You add the two numbers together: 24 + 60 = 84.
The answer is already there: 60 is the total. Take the number you know away from it to find the missing part.
Tips
- Always check: put your number in place of the dot and work out the sum.
Why it works
An addition with a dot is the opposite of a normal addition. You already know the answer, and you look for the part that is missing. You work back from the answer with a subtraction.