Expectation of rolled dice

[vicki]

A math professor is betting his entire fortune, $20,000, on one roll of
(two) dice. If the total is 7 or 11, he will take home $100,000, otherwise
he forfits his savings. What is his mathematical expectation?

(I came up with 6,400-but I guess this is not completely correct, please help)

[Adrian]

For 2 dice, there are 6*6=36 combinations possible.
To get a total of 7, we can have 16, 61, 25, 52, 34, 43, that's 6 out of 36 combinations.
To get a total of 11, we can have 56, 65 thats 2 out of 36 combinations.

P(7 or 11)=(6+2)/36=0.2222

expectation=100000*0.2222 + 0*(1-0.2222)=22,222

[Koumar]

For 2 dice, there are 6*6=36 combinations possible.
To get a total of 7, we can have 16, 61, 25, 52, 34, 43, that's 6 out of 36 combinations.
To get a total of 11, we can have 56, 65 thats 2 out of 36 combinations.

P(7 or 11)=(6+2)/36=0.2222

expectation=100000*0.2222 + 0*(1-0.2222)=22,222

Is this correct?

I make it for 36 rolls the guy lays out 720k (36 x 20k) and gets back 800k (8 x 100k) when successful

Hence he wins 80k for every 36 rolls

so for 1 roll he expects to make $2222.22

[aksingh]

A math professor is betting his entire fortune, $20,000, on one roll of
(two) dice. If the total is 7 or 11, he will take home $100,000, otherwise
he forfits his savings. What is his mathematical expectation?

P(WIN) = 8/36, P(LOSS) = 28/36
EV($20000 on 7 or 11) = 100000x(8/36) + (-20000) x (28/36)
= (800000 - 560000)/36 = 240000/36 = $66666.67