Looking at the pie charts
Just looking at the second pie chart, Rayfield had the most passes - more than a quarter of all passes.
However, if you look at the first pie chart, you can see that a lot of people took their test at Rayfield (around a quarter), so you would expect a lot of people to pass.
What we are interested in is the number of people who passed relative to the number of people who took their test there - so the centre where the wedge on the second pie chart is largest relative to its wedge on the first pie chart - which is Mallick.
Working out the pass rates
Using the numbers from the pie charts, we can find the pass rates for each centre.
This is the percentage of tests which were passed:
We can see that Mallick has the highest pass rate.
Other ways of respresenting the data
Bars showing tests taken and passed at each centre:
Pie charts showing passes and fails at each centre (fails must be found as the difference between tests taken and passes):