I looked at the HARD section and as it’s a long time ago that I was playing with this stuff it took a little while before concluding “can’t be done’. I checked the AND/OR document, it’s RUBBISH.
prob(A) =1/2, prob(B)=3/4, so prob(A or B) = 5/4.
Was this a test?

Events have to be mutually exclusive for the OR rule to apply, and independent for the AND rule to apply. I suppose there could be an additional sentence in the HARD section asking to assume independence for AND rule and mutually exclusive for OR rule.

I looked at the HARD section and as it’s a long time ago that I was playing with this stuff it took a little while before concluding “can’t be done’. I checked the AND/OR document, it’s RUBBISH.

prob(A) =1/2, prob(B)=3/4, so prob(A or B) = 5/4.

Was this a test?

where are you getting those fractions from on the worksheet??

Events have to be mutually exclusive for the OR rule to apply, and independent for the AND rule to apply. I suppose there could be an additional sentence in the HARD section asking to assume independence for AND rule and mutually exclusive for OR rule.

edit: I’ve added the sentence!

But what about the general rule:

P(A or B) = P(A) + P(B) – P(A and B)

Is this not considered at all in the exposition?

Not at GCSE. Maybe in A Level Stats? No P(B|A) stuff either.