1 on the x-axis (number of days) 2 units on the y-axis (number of texts sent)
When we are working with graphs, it is important we pay close attention to the scale, axes, label and title – or SALT.
Scale: Choose horizontal and vertical scales that will accurately show the data. Axes: On each axis, the scale is clearly shown and increments (values) evenly spaced.
Label: Label each axis identifying the data shown and the units used. For example, ‘number of days’ and ‘number of messages sent’. Title: The title should explain the purpose of the graph. For example, ‘Graph of John’s messages over 6 days’.
It is important to remember that graphs can go down as well as up. We read graphs from left to right. When a graph moves in a downward direction, it is representing a decreasing pattern. We draw this graph exactly the same way as an increasing pattern.
Worked example 3 Fiona has €18 on Sunday night. From Monday, she must spend €3 per day on lunch for fi ve days.
(i) Create a table to show how Fiona’s money is decreasing each day.
(ii) Draw a graph to show this information.
(iii) Will Fiona have enough money to buy lunch for 8 days? Explain your answer.
Solution (i)
Amount of money remaining per day y
15 16 17 18
10 11 12 13 14
9 8
7 6 5 4 3 2 1
0 1 112 2 3 4 5 6 Number of days Linking Thinking 1 7 8 x