what are the odds against tossing a 7 or an 11 in a single throw pair of dice.
prob(7) = 1/6
prob(11) = 2/36 = 1/18
let X be the event of throwing a 7 or 11
prob(X) = 1/6 + 1/18 = 2/9
prob(notX) = 7/9
odds against X = 7/9 : 2/9
= 7 : 2
prob(11) = 2/36 = 1/18
let X be the event of throwing a 7 or 11
prob(X) = 1/6 + 1/18 = 2/9
prob(notX) = 7/9
odds against X = 7/9 : 2/9
= 7 : 2