The following mistakes could be explained observed from the plotted bar chart presented in the attachment :
1.) The numeric label of the y-axis which shows the number of text messages isn't well scaled, the numbering did not start from 0, hence this is a defect in the scaling of the bar chart.
2.) Looking closely, the plotted bars do not ALIGN well in terms of spacing as the interval between each bar isn't consistent.
3.) Both the x and y axis of the graph are t labeled thus failing to add a good and meaningful description to the plot especially for first time viewers.
You cut the arc measure 100 degrees in half. This is using the inscribed angle theorem. The angle 'a' is the inscribed angle that cuts off this 100 degree arc.
