The probability of being solved by A or B is 0.36, then the probability of not being solved is 1-0.36 = 0.64.

If the probability of the solution of a and b is p, then: (1-p)? =0.64, so: p=0.2

The number of people who solved this problem is: x 1 x2 x3.

0 1 2

Probability (1-p)? C( 1，2)( 1-0.2)×0.2 p？

P(x 1) P(x2) P(x3)

Then e (x) = (x1) × p (x1)+(x2 )× p (x2)+(x3 )× p (x3).