Like desires I have a degree in Mathematics and it is very rare I use anything above what I believe would be KS3 level never mind GCSE (topics below pasted from BBC). In fact even in cases where some more advanced maths is required (on a not so frequent basis), you could make a case that it would be more efficient for people to look up / get help with such problems than having spent all that time learning the skills. Much as we do with other things in life , we effectively subcontract it out to other people who have the skills (trademen, mechanics, medical professionals, specialists in the workplace...).
Going slightly OT here but I have said for a while that schools should let pupils choose specialisms at an earlier age, I wasted years at school doing subjects of no interest / use to me. After 2-3 years of secondary school you should have enough experience to form an opinion IMO.
Number
Calculations, orders of operation, fractions, decimals, and percentages
Algebra
Formulas, inequalities, equations, coordinates, graphs and sequences
Handling data
Recording and representing data, measures of average, probability and relative frequency
Measures
Reading and converting measurement units, perimeter, area, volume and time
Shape and space
Shapes, transformations, angles, triangles, lines, polygons, symmetry, circles, pythagoras' theorem
.
I found that I always overthought them all and that was what really barred me from going further. Plus it barred me from actually understanding what was going on.
