Single-Digit Addition and Subtraction quiz

More questions about Single-Digit Addition and Subtraction

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1. 1 Easy

   What single-digit value remains when subtracting 7 from 9?

   Answer: 2

   Why: In Johannes Widmann's 1489 German business arithmetic the minus sign marked a deficit; its use for subtraction is attested in 1518.

2. 2 Medium

   Why does reversing the order in single-digit subtraction change the result?

   Answer: Subtraction is non-commutative

   Why: While addition is commutative ($7 + 2 = 2 + 7$), swapping subtraction order inverts the sign: $7 - 2 = 5$ but $2 - 7 = -5$.

3. 3 Hard

   What term describes repeatedly summing digits to one single digit?

   Answer: Digital root

   Why: The digital root always matches the number's value modulo 9, except multiples of 9 yield 9.

4. 4 Easy

   What is the largest total you can reach by adding two single-digit numbers?

   Answer: 18

   Why: The 18 ceiling is why adding two numbers in columns never carries more than a single unit into the next place value.

5. 5 Medium

   What is a set of four equations built from three numbers called?

   Answer: Fact family

   Why: A fact family with two identical addends, such as $4 + 4 = 8$, contains only two unique equations instead of four.

6. 6 Hard

   Which three distinct single digits have a sum of 24?

   Answer: 7, 8, 9

   Why: Because 7, 8, and 9 are the three largest single digits, their sum of 24 is the maximum possible for three distinct digits.