"maths" is not "arithmetic"
'the first thing you have to realise is that "maths" is not "arithmetic" as many might believe'
I did Maths A and S levels, but those contained a fair bit of arithmetic. It wasn't until I did Maths at uni that I fully realised the truth of the above quote.
I quickly discovered that the only times I used mental arithmetic in earnest was when shopping or playing darts.
The desire to maintain my skills in arithmetic justified the purchase of a dart board. :-)