Minds On
Missing numbers
When we see an addition or subtraction statement, the equal sign lets us know that the numbers on both sides total the same amount.
If the statement is
1 + 3 = (Blank)
the answer must be 4 because the equal sign means both sides are the same.
If the statement is
2 + (Blank) = 3
the equal sign means both sides are the same so the (Blank) represents the number 1.
Let’s explore this video as teacher Shahana helps us to find missing numbers.
Let’s review what teacher Shahana showed us.
(Blank) + 2 = 1 + 5, or something increased by 2 is equal to 1 increased by 5.
We know that 1 + 5 = 6, so now we know that
(Blank) + 2 is equal to 6
One strategy to find the mystery number would be to add up from 2 by 1s or 2s to find 6.
The missing number is 4.
Those mystery numbers or unknown values have a special name. They are called variables.
Here they were represented with a (Blank)
Action
Breaking news!
The Number Hall of Fame is missing some famous numbers.
The Hall of Fame staff are working as quickly as possible to find them, but it is challenging.
Help find the missing number to replace the variable and repair these addition and subtraction statements so that the equal sign can keep its promise.
You may wish to use counters, blocks, or another method of your choice to help you figure out the value of the variable or missing number.
Record your ideas in a notebook or a method of your choice.
Addition
5 + 2 = 3 + (Blank)
Press the ‘Answer’ to reveal the answer to this problem.
5 + 2 = 3 + 4
The missing number is 4.
7+ 4 = (Blank) + 6
Press the ‘Answer’ to reveal the answer to this problem.
7+ 4 = (Blank) + 6
11 = 5 + 6
The missing number is 5.
4 + 3 = (Blank) + 1
Press the ‘Answer’ to reveal the answer to this problem.
4 + 3 = (Blank) + 1
7 = 6 + 1
The missing number is 6.
Now try and fix these statements.
They have a variable or missing number on the left side of the equal sign.
5 + (Blank) = 7 + 3
Press the ‘Answer’ button to access the answer to this problem.
5 + (Blank) = 7 + 3
5 + (Blank) = 10
The missing number is 5.
(Blank) + 4 = 11 + 3
Press the ‘Answer’ to reveal the answer to this problem.
(Blank) + 4 = 11 + 3
(Blank) + 4 = 14
The missing number is 10.
4 + (Blank) = 7 + 9
Press the ‘Answer’ to reveal the answer to this problem.
4 + (Blank) = 7 + 9
4 + (Blank) = 16
The missing number is 12.
Subtraction
Let’s try and repair some subtraction statements. Record your answers in a notebook or a method of your choice.
5 − 2 = (Blank)
Press the ‘Answer’ to reveal the answer to this problem.
5 − 2 = 3
The missing number is 3.
18 − 6 = 10 + (Blank)
Press the ‘Answer’ to reveal the answer to this problem.
18 − 6 = 10 + (Blank)
12 = 10 + (Blank)
The missing number is 2.
12 − 10 = (Blank)
Press the ‘Answer’ to reveal the answer to this problem.
12 − 10 = 2
The missing number is 2.
Now let’s find some missing numbers with variables on the left side of the equal sign.
(Blank) − 1 = 3 + 12
Press the ‘Answer’ to access the answer to this problem.
(Blank) − 1 = 3 + 12
(Blank) − 1 = 15
The missing number is 16
16 − (Blank) = 4 + 9
Press the ‘Answer’ to reveal the answer to this problem.
16 − (Blank) = 4 + 9
16 − (Blank) = 13
The missing number is 3.
10 − (Blank) = 15 − 7
Press the ‘Answer’ to reveal the answer to this problem.
10 − (Blank) = 15 − 7
10 − (Blank) = 8
The missing number is 2.
Consolidation
Give it a try
Balance the following equations by finding the missing number.
Remember to make sure the equal sign keeps its promise.
You may wish to have some counters, use the interactive balance, or use a whiteboard to help you figure out the value of the variable or missing number.
For each missing number question, select the missing number from the drop-down menu.
Missing number
Let's create a missing number question on your own.
Record your ideas in a notebook or a method of your choice.
Reflection
How do you feel about what you have learned in this activity? Which of the next 4 sentences best matches how you are feeling about your learning? Press the button that is beside this sentence.
I feel...
Now, record your ideas about your feelings using a voice recorder, speech-to-text, or writing tool.