Constant Difference
Constant Difference:
A subtraction strategy where the difference between two numbers does not change after adding or subtracting both of them with the same number.
Videos for Educators
Important Information: Once students understand that subtraction is the difference between two numbers, they can begin to investigate what would happen if both numbers are changed by the same amount. Having students explore this relationships with smaller number such as 5-3, may help them build this understanding.
Students need to understand that constant means something stays the same or does not change.
Students need to understand that difference means the distance between two numbers.
Adding or subtracting the same quantity from both numbers maintains the difference between the numbers. This will allow students to manipulate the numbers to create friendlier equations.
Examples of what kids might do:
Examples of what students might say: "I know its easier to subtract from a number with zero so I took away two from 52 and two from 39. I then did my subtraction and got 13."
Strategies to Support Student Learning:
Pose the following questions: Start with 5 - 3, if we add 2 to each side, what happens to our answer? 5-3 becomes 7-5. Is the answer the same? What is we subtract 2 from both sides? 5-3 becomes 3-1. Is the answer the same?
Practice this strategy using a numberline