h=.5
t=.5
all.heads=.5^10
all.heads=h^10; all.heads
all.tails=t^10; all.tails
at.least.1.tail=1-all.heads; at.least.1.tail

pb=.8; j=.89; pbandj=.78
j.given.pb=pbandj/pb; j.given.pb