Answer:
45 from 3 questions
3 x 15 = 45 answers
Shown below for one question then all you need to do is multiply them all by 3 as in (15 x 3)
A
B
C
D
AB
AC
AD
BC
BD
CD
ABC
ACD
ABD
BCD
ABCD
This gives a probability that some one who dont know how many to answer in one question gets 1/45 probability they will get the right answer.
