Log tables and maths WITHOUT a calculator - those were the days!
At least we could do numbers in our heads, don't have to reach for a calculator to work out 10% of 200.
Joking apart, as an ATPL instructor I find this is THE weakest link for most students. Regretfully it is a sad reflection on the English (lack of) education system and exams that are now little short of a joke.
As stated below go and work in shop/bar you'll soon pick up some essential key skills. One of my best students at numbers used to work in a bazaar in Algeria.