What is the probability that if a coin lands on heads and the number cube shows 5

For the coin it is one minus the probability of the coin landing on tails minus the tiny probability of the coin landing on its edge and balancing there. So something like (1 - 0.499 999 5 - 0.000 001), or 0.499 995; call it as near 0.5 as makes no difference.

For the number cube it is one minus the probability of the cube landing on one, three or five minus the tiny probability of the coin landing on an edge or the even tinier probability of it landing on a corner and balancing there. So something like (1 - 3 * 0.166 666 - 12 * 0.000 000 36 - 8 * 0.000 000 08) , or 0.499 998; call it as near 0.5 as makes no difference.

So the joint probability is the first probability times the second. So 0.5 * 0.5 which is 0.25 for all intents and purposes

(copied from Quora)