Solution :
Let A = Economics, B = Mathematics
n(A) = 311, n(B) = 243, 
a). So, 
= 311 + 243 - 135
= 419
b). n(A only) = 311 - 135
= 176
n(B only) = 243 - 135
= 108
Exactly one of these two courses

= 0.568
c). Neither economics nor mathematics


= 0.162
Sizes? Of the wall and paper?
Yes, they are independent. First of all, we know that P(A) = 1/4, P(B) = 2/5, and P(A and B) = 1/10. To know if two events are independent, the following questions must be true: P(A)*P(B) = P(A and B). So since (1/4)*(2/5) = 2/20 which equals 1/10, these events are independent
There's really no way to write this equation as a word problem .