Overview:
Subtraction is a basic arithmetic operation. Variables, as well as more familiar numbers, can be subtracted using similar models, of take-away, the number line, and comparison.
What Is the Take-Away Model of Subtraction?
The take-away model of subtraction is the model that is most familiar from elementary school. Recall familiar problems such as “If Harry had 30 marbles and 10 were taken away by his friend Ron, how many were left?” In symbol form, that problem would be 30 – 10 = 20, which might have been read as “30 take away 20”. Similarly, if Meg had 45 math problems in an assignment and she finished x of them, the expression would be 45 – x.
What Is the Number Line Model of Subtraction?
In the number line model, the number line can be extended so as to include both positive and negative real numbers. On the number line, subtraction is accomplished by starting with one number and moving to the left. Suppose that the high temperature is 60o F and the low for the day is 31o F. In symbol form, that problem would be 60 – 31 = 29. Since subtraction is the same thing as adding a negative number, the problem could also be expressed as 60 + -31 = 29.
What Is the Comparison Model of Subtraction?
In the comparison model of subtraction, the number to be subtracted is compared with the number to be subtracted from. That comparison is called the difference. In mathematical terms using variables, x – y means how much more x is than y. Suppose there are 380 cars in a parking lot on Monday and 370 cars in the same parking lot on Tuesday. In symbol form, the difference between cars in the parking lot on the two days is 380 – 370 = 10.
What Types of Problems Can Be Solved by Subtraction?
Some of the problems that can be solved by subtraction include questions of population change or growth. Suppose that the population of Anytown was 15000 in 2000 and 17300 in 2010. The difference is 17300 – 15000 = 2300 or a growth of 2300. However, if the population of Anytown were 17300 in 2000 and 15000 in 2010 the difference would be 15000 – 17300 = a loss of 2300, or -2300. Similarly, if a savings account has $500.00 in it and W dollars are withdrawn, the amount remaining is $500.00 – W.
Interested in pre-algebra tutoring services? Learn more about how we are assisting thousands of students each academic year.
SchoolTutoring Academy is the premier educational services company for K-12 and college students. We offer tutoring programs for students in K-12, AP classes, and college. To learn more about how we help parents and students in Brockton, MA: visit Tutoring in Brockton, MA