Finding the Missing Number
What is a Missing Number?
Sometimes we have a math problem with a box or letter. We need to find what number goes in the box!
We use x to show the missing number.
Addition Problems
When we add numbers and one is missing:
x + 3 = 7
This means: What number plus 3 equals 7?
How to solve:
Take away the number we know from the answer.
x = 7 - 3
x = 4
When the Missing Number is Second
Sometimes the missing number comes after the plus sign:
5 + x = 8
This means: 5 plus what number equals 8?
How to solve:
Take away the number we know from the answer.
x = 8 - 5
x = 3