The line graph shows the rain at a weather station each month from January to July, in millimetres: 120 in January, 110 in February, 30 in March, 80 in April, 50 in May, 100 in June and 90 in July. What was the average rain per month from March to July?
Average = 350 ÷ 5 = 70 mm
Ans: 70 mm
How to solve it
Decide what counts as data: the months the question asks for, not every month on the graph.
Count them: March to July is 5 months, so there are 5 pieces of data.
Read those 5 months off the graph: 30, 80, 50, 100 and 90 millimetres.
Add them in order: 30 plus 80 plus 50 plus 100 plus 90 is 350.
Divide the total by the number of data: 350 divided by 5 is 70 millimetres.
5 months, 5 pieces of data. 350 divided by 5 is 70. Count the data first. Then divide.
Practice questions with worked solutions
Question 1 is free to try. The other 6 open in the free trial, each with its full working.
Question 1 of 7 · Basic · free to tryThe line graph shows the number of customers in a bookshop at each hour from…The line graph shows the number…
The line graph shows the number of customers in a bookshop at each hour from 11 a.m. to 5 p.m. The readings were 25 at 11 a.m., 31 at 12 noon, 38 at 1 p.m., 40 at 2 p.m., 34 at 3 p.m., 28 at 4 p.m. and 22 at 5 p.m. What was the average number of customers per hour from 1 p.m. to 4 p.m.?
number of data = 4 (1 p.m. to 4 p.m. is four readings)
total = 38 + 40 + 34 + 28 = 140
average = 140 ÷ 4 = 35 customers
Answer: 35 customers
For parents
How do you solve average from a graph questions in P6?
Here the data comes from a graph or table rather than a list.
What your child learns here
Here the data comes from a graph or table rather than a list. Your child learns to decide which readings count before adding, and to count the number of data carefully. Graphs that show a running total are covered too.
Read values off a bar graph, line graph or table.
Use only the readings the question names, not every one on the graph.
Count inclusive ranges correctly, such as March to July being 5 months.
Find a value the graph does not show, using the average and the total.
Does the answer make sense?
An average must lie between the lowest and highest readings it is taken from. On a graph showing a running total, your child should use the rises from hour to hour, not the heights of the points, so the average flow cannot be more than the biggest single rise.
How to practise these questions
The Basic questions train reading values off a graph and dividing by the right number of items over the range asked. Intermediate questions add graphs that keep a running total, or that have no numbers on one axis. Challenge questions read only part of a running total graph, or combine a pie chart with different rates. When reading an average off a graph is hard, read the written step-by-step solution together.
Questions parents ask
How do you find an average from a line graph? Read the values the question asks for, add them, and divide by how many readings you used. Only the readings named in the question count.
How many months are there from March to July? Five: March, April, May, June and July. Minusing the month numbers gives 4, which misses one, so count the months by name.
Is reading graphs part of the Primary 6 average outcomes? The Primary 6 average outcomes cover average as total value ÷ number of data. In these questions the graph or table is where the data comes from, using graph skills taught in earlier years.
