Finding a Missing Addend
Finding a missing addend uses the inverse relationship between addition and subtraction: if part + missing = total, then missing = total minus part. In Grade 6 Saxon Math Course 1 (Chapter 1: Number, Operations, and Algebra), students apply the formula x = b - a to any equation of the form a + x = b. For example, if Maria baked some cookies in the morning and 14 more in the afternoon, making 31 total, write x + 14 = 31, so x = 31 - 14 = 17. Students recognize this pattern in word problems and algebraic equations, building the foundation for solving one-variable equations.
Key Concepts
Property To find a missing addend, subtract the known addend from the sum. For an equation $a + x = b$, the unknown is found by $x = b a$.
Examples To find $x$ in $x + 22 = 50$, you calculate $x = 50 22$, so $x = 28$.
To find $y$ in $35 + y = 75$, you calculate $y = 75 35$, so $y = 40$.
Common Questions
How do you find a missing addend?
Subtract the known addend from the sum: if a + x = b, then x = b - a.
Solve x + 14 = 31.
x = 31 - 14 = 17.
Solve 25 + n = 63.
n = 63 - 25 = 38.
Why does subtracting the known addend find the missing one?
Addition and subtraction are inverse operations. Subtracting the known part from the total undoes the addition and leaves only the missing part.
A bag had some apples; 9 more were added to make 22 total. How many were in the bag originally?
x + 9 = 22. x = 22 - 9 = 13 apples.