Line graphs

Line graphs

A line graph represents the relationship between two variables such as blood group and age, or number of events and time. A line graph uses lines to show the relationship between two variables in the x-axis and y-axis. The line graph normally includes the units of a physical quantity represented in the graph. For example, when the line graph represents mass in one axis, the unit of mass like ton, kilogram or gram is shown along that axis. Line graphs can be used in hospitals to show clinical results, in schools to display the pupil's marks and in business to show sales of different commodities.

Reading and interpreting line graphs

Example

Study the following graph, and then answer the questions that follow.

(a) Mention the scale of the graph in the x-axis and y-axis.

(b) What was the price of 1 kilogram in 2008?

(c) In which years was the price of beans 1,000 shillings?

(d) Mention the years in which the price of beans did not change

(e) In the year 2003, a family bought 50 kilograms of beans. How much money did the family spend?

Answers

(a) The horizontal line (x-axis) represents sales of beans in a year. Scale: One unit represents one year.

The vertical line (y-axis) represents the price of beans in shillings. Scale: One unit represents one thousand shillings.

(b) To get the cost of one kilogram of beans, read the point where 2008 is located on the x-axis. Move upwards along the y-axis until you meet the line. Move leftwards to the y-axis, read the price of one kilogram of beans. The value of y-axis is sh 2 × 1,000 = sh 2,000. Therefore, the price of 1 kilogram of beans was 2,000 shillings.

(c) To get the years in which the cost of one kilogram of beans was 1,000 shillings, read the point where 1,000 shillings is located on the y-axis. Move rightwards until you meet the line, then move downwards to meet the x-axis and read the year. The years with this price were 2000, 2004 and 2007. Therefore, the years where the cost of one kilogram of beans was 1,000 shillings were 2000, 2004 and 2007.

(d) The points within the line graph which lie in the same line along the x-axis had the same price. Therefore, the two years which had the same price are 2001 and 2002.

(e) In the year 2003, the price of beans was 3,000 shillings. Multiply the number of kilograms by the price of one kilogram of beans.

Thus, 50 kg × sh 3,000 per kg = sh 150,000. Therefore, the family paid 150,000 shillings.