"Odds of your bomber being shot down on or before the 5th sortie: 1/6 + 1/6 + 1/6 + 1/6 + 1/6 = 5/6 "
thats not true at all. u have to use a multiplicative connection in this case: the odds of the bomber performing strat.bomb successfully are 5/6. U are going for 5 runs. So the result is 5/65/65/65/65/6 = (5/6) ^ 5 ~ 40%
u have a probability of 40% to strike for 3,5*5 = 17,5 IPC at costs of 15 IPC. which still isnt a good deal imho…