1. Subtraction Word Problems With Missing Numbers
Mathematics 2 Ms. Meek
Subtraction Word Problems With Missing Numbers

2. Review: Subtraction With Missing Numbers
A subtraction problem has at least two number amounts, the smaller amount is taken away from the larger amount, and a difference. If we know one number, and we know the difference, we can also learn to solve for the other number.

3. Subtraction With Missing Numbers
Often times, when we are given a problem with a missing number, there is something called a variable put in the place of that missing number. A variable represents a missing number. Example: 14 - X = 6  variable

4. Solving for the Missing Number
When solving for the missing number, first set the problem up vertically. We “subtract down to find the bottom number and “add up” to find the top number.
Subtract Down
Nine minus six
Equals three.
Add Up
Three plus six
Equals nine.
9 -6 3

5. Solving for the Missing Number
Example: 14 – n = 6
Subtract Down
Fourteen minus what number
Equals six?
Add Up
Six plus what number equals fourteen? n 6

6. Solving for the Missing Number
Often it is easier to find a missing number by “adding up”. If we add 8 to 6 we get 14, so the missing number is 8. We can check our answer by replacing n with 8 in the original problem.
Subtract Down
Fourteen minus what number
Equals six?
Add Up
Six plus what number equals fourteen? n 6

7. Missing Number Word Problem
Today we will practice solving word problems in which the difference is given and one number is missing.
We can solve these just like problems that have a missing number, we subtract down if we are missing the bottom number, and add up if we are missing the top number.

8. Missing Number Word Problem
Example:
Walter had 8 marbles. Then his brother Lamont lost some of his marbles. Walter now has 3 marbles now. How many marbles did Lamont loose?
If we can recognize the plot, we can write a number sentence to solve the problem.

9. Missing Number Word Problem
We know Walter had some marbles, then some were lost (taken away).
This problem has a “some-some went away” plot so it can be represented with a subtraction formula.
We know the “some” number and we know the difference. So, we put these numbers into the same formula.
Formula: Some – Some went away = difference
Problem: 8 - x marbles = 3 marbles

10. Missing addend Word Problem Eight minus what number
Formula: Some – Some went away = difference Problem: 8 - x marbles = 3 marbles To solve, write the problem vertically. 8 -m 3 m = 5 Plug 5 into the problem to check.
Add Up
Three plus what number
Equals eight.
Subtract Down
Eight minus what number
Equals three?

11. Conclusion
A subtraction problem has at least two number amounts, the smaller amount is taken away from the larger amount, and a difference.
If we know one number, and we know the difference, we can solve for the other number.
When solving, first set the problem up vertically.
We can “subtract down” or “add up” to find the missing number.
We can solve word problems just like problems that have a missing number.