Using a Known Fact

Videos for Educators

Important Information:

A powerful strategy for children to possess is using facts that they know to assist them in determining the answer to facts that they do not know. Common known facts may include making 10 facts and doubles facts. Students may use these known facts as a starting point to solve unknown equations. For example, a student who has become comfortable making 10 may using the following strategy to solve 6 + 3. They may recall that 6 + 4 = 10 and start with that. Knowing 3 is 1 less than 4, they may subtract 1 from their final answer to get 9.

Students may also use known double facts to help solve an unknown equation. For example, 15 + 16 may be looked at as 15 + 15 = 30. The student knows that 16 is one more than 15 and add one to the final answer.

Having students spend time working with making 10 and doubles facts will give them another tool to solve addition and subtraction equations that may be more difficult.

Examples of what students might do

Examples of what students might say:

"I know that seven plus three is 10. I added one more to make 11."

"I know that ten plus six is 16 and 10 is one more than 9. So I subtracted 1 from my answer."

Strategies to Support Student Learning

• Students who are using the known fact strategy are developing relational reasoning. They are beginning to work with numbers in more efficient and flexible ways, relying less on counting. They are continuing to build on part-whole relationships, recognizing that a first number (or part), plus a count of the second number (part), will give them the total amount (whole).

• As students build on their strategies for working with numbers in more and more flexible ways, they can begin to develop other strategies such as decomposing one or both addends to find anchors of five, for example 6+7 =(5+1) +(5+2)and then onto up and over 10, for example 7+5=(7+3) +2.