Subtracting Integers
Subtraction is a basic algebraic operation where we take one number away from another. If we had \(9\) chocolates, and someone took \(3\) chocolates away, we would have \(6\) chocolates left. This is expressed as
\[ 9 - 3 = 6. \]
Note that when we subtract a large number from a small number, we will have a negative number. So \( 8 - 10 = -2 \).
When subtracting numbers with more than one digit, it is sometimes necessary to decompose the larger unit. For example, in \( 35-9\) we want to subtract \(9\) units, but there are only \(5\) units available in \(35\). To solve this, we take one of the tens and break it into units which gives us \(20\) in tens and \(15\) units. \( 15-9 = 6 \) so the result is \(26\).
What is \( 23 - 9 \)?
We have \[ \begin{array} { r r r } & \not 2 ^ 1 & ^1 3 \\ - & & 9 \\ \hline & 1 & 4 \\ \end{array} \]
Thus \( 23 - 9 = 14 \). \( _\square \)
What is \( 37-4 ?\)
We have \[ \begin{array} { r r r } & 3 & 7 \\ - & & 4 \\ \hline & 3 & 3 \\ \end{array} \]
Thus \( 37 - 4 = 33 .\) \( _\square \)
What is \( 121 - 17 ?\)
We have \[ \begin{array} { r r r } & 1 & \not 2 ^1 & ^1 1 \\ - & & 1 & 7 \\ \hline & 1 & 0 & 4 \\ \end{array} \]
Thus \( 121 - 17 = 104 .\) \( _\square \)
What is \( 2-17 ?\)
When we subtract a large number from a small number, we have a negative number. Since \(17-2\) is
\[ \begin{array} { r r r } & 1 & 7 \\ - & & 2 \\ \hline & 1 & 5 \end{array} \]
thus \( 2 - 17 = -15 .\) \( _\square \)
What is \( 27 - 35?\)
When we subtract a large number from a small number, we have a negative number. Since \(35-27\) is
\[ \begin{array} { r r r } & \not 3^2 & ^1 5 \\ - & 2 & 7 \\ \hline & & 8 \end{array} \]
thus \( 27 - 35 = -8 .\) \( _\square \)