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**Revilo** First little piggy is 25% likely to go to market if second little piggy goes. Second little piggy is 50% likely to go to if first little piggy goes. Sadly at least one of them must go to market. How likely are they both to go?

So far i have:

Let A = First little piggy goes to market

B = Second little piggy goes to market

P(A given B) = 0.25

P(B given A) = 0.5

P(A union B) = P(A) + P(B) - P(A intersection B)

Is the P(A union B) = 1 as atleast one must go, so this is always true?

Does anyone have any ideas, i'm really stuck.