Answer
a) Sum of all percentages in less than $100\%$; a region misses;
b) The bar graph is easier to interpret\\
Work Step by Step
a) We add the percentages of each area:
$15.2\%+15.2\%+24\%+27.2\%+6\%=87.6\%$
An error is that the sum of the percentages is not $100\%$.
The missing percentage is:
$100\%-87.6\%=12.4\%$
The areas of different regions of the circle should be directly proportional to the percentages they show. The missing part should be represented by an area approximately half the area of the ASDA region.
b) The mode shows regions that have the same area. Represented in a pie graph, two area having the same area/percentage should have the same value for the center angle, while in a bar graph it is much easier to compare the heights of two bars.
