What is the term for a set of related addition/subtraction or multiplication/division equations that use the same numbers?

• A. Fact family
• B. Equation set
• C. Number line
• D. Expression

Answer: (A)

Think about how numbers relate when you add and subtract or multiply and divide. A fact family is a group of related facts that use the same three numbers. They show how the operations connect: with addition and subtraction, the two addends and the total form the trio, so you can write 3 + 5 = 8, 8 − 5 = 3, and 8 − 3 = 5. With multiplication and division, the same idea applies: 2 × 3 = 6, 6 ÷ 3 = 2, and 6 ÷ 2 = 3. Seeing these together helps you understand how the operations undo each other. The other terms don’t fit as well: an equation set is just a collection of equalities, a number line is a visual tool, and an expression is a mix of numbers and operations that may not show the inverse relationships.