What does "hard sums" mean?
"Hard sums" is used to mean "difficult mathematics" in a self-deprecating way, depending on the speaker.
If someone says
I can do hard sums.
and they are:
- A four year-old: It means they've started doing addition.
- An eight year-old: It means they've mastered multiplication.
- A high-school student: It means they can do some simple calculus.
- An undergraduate: It means they can do more complex calculus / analysis / algebra.
- A post-graduate: It means they're Einstein. :-)
And each group is more self-deprecating than the last.