Subtracting Whole Numbers
Subtraction of whole numbers is used by everyone. For example, to find the sale price of an item, a store clerk subtracts the discount from the regular price. To measure climate change, a scientist subtracts the high and low temperatures. A trucker subtracts odometer readings to calculate the number of miles driven on a trip.
To subtract two whole numbers, think of taking away objects from a set. For example, if we start with a set of 9 stars and take away a set of 4 stars, a set of 5 stars is left.
If the subtraction of the digits in any place value column requires that we subtract a larger digit from a smaller digit, we must borrow or regroup
To describe the special relationship between addition and subtraction, we say that they are inverse operations
Estimation is used to find an approximate answer to a problem
To answer questions about how much more or how many more, we use subtraction
To evaluate (find the value of) expressions written in horizontal form that involve addition and subtraction, we perform the operations as they occur from left to right