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Worksheet Worksheet 4
A4US

1.

There is a way to leverage your addition experience for doing subtraction problems. It require reframing the idea of subtraction as solving an addition algebra problem. Notice that the following two equations are equivalent to each other.

\begin{equation*} x = 100 - 48 \qquad 48 + x = 100 \end{equation*}

The first question asks, "What is the result of subtracting 48 from 100"? The second question asks, "48 plus what number is equal to 100?" While the answers will be the same, they represent two different approaches. We will focus on the second one. Here is a diagram for that question:

Rather than trying to count down from \(b\) by the amount \(a\text{,}\) this is now about counting up from \(a\) to \(b\text{.}\) The application of this is most common when the value \(b\) is a "nice" value to work from. The reason is that it's mentally easier to break it down into different parts using the place values as a guide. Here are two diagrams for \(100 - 48\text{,}\) each showing a different visualization:

Which of the two calculations at the bottom is more intuitive for you?

2.

Mentally apply the above method of subtraction to perform the following calculations.

\begin{equation*} \begin{aligned} 100 - 28 \amp = \\ 100 - 77 \amp = \\ 100 - 31 \amp = \\ 150 - 48 \amp = \\ 150 - 87 \amp = \\ 150 - 95 \amp = \\ 300 - 153 \amp = \\ 800 - 418 \amp = \\ 600 - 238 \amp = \\ 1000 - 275 \amp = \\ 1000 - 318 \amp = \\ 1000 - 444 \amp = \end{aligned} \end{equation*}