Question

how to calculate passing marks

Answer 1

see passing marks on the site of school and divide it by 100

Answer 2

if you mean in a test quiz the formula is this:
correct answers ✖ 3 _ uncorrect answers divided by number of questions ✖ 3
if we suppose true answers with t
wrong with w
and all with a
we got:
$(t \times 3 - w) \div a \times 3$