20-30% as mentioned.
The reality of the UK education system is you need at least BBB at A level or equivalent to qualify on a course for a "good" university.
I'm pretty certain that statistically 30% of all A level students roughly earn themselves a B in a designated subject, obviously it varies per subject though. For example a B in something like History is always going to be worth more than an A in media studies.
Round about 20% will get themselves an A grade as well so yes, 20-30 sounds about right.
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