Mathematics and Economics at LSE

One of my friends decided to switch to Accounting and Finance in the second year from Mathematics and Economics. He complained that Maths at LSE is very difficult at LSE.
My friend got 98% for GCE AS/A2 Maths, 96% for Further Maths and 92% for Economics
But I don't understand why he finds it difficult.
Can you please say me do most of Math and Econ students change their degree in the same way?
Do most of the Math and Econ students have to put most of time to their studies abd have less time to socialise and take part in extra curriculars?
My friend also complained that most Math and Econ students fail exams and gat bad grades is this true?
He saya abstract Maths is really difficult.

Guys can you please give em an answe to these questions,because I'm also looking forward to get into LSE to do the same course.