Your friend claims the coin is fair, but you aren't convinced. You can't prove for certain that your friend's coin is weighted unfairly (without special equipment, of course), but you can test your hypotheses with a sample of coin flips. If the proportion of heads in your sample is high enough, it provides strong evidence that your friend's coin is weighted in their favor. In other words, a high enough proportion of heads would be sufficient evidence for you to reject the assumption that your friend's coin is fair. Let's suppose you grab your friend's coin and you flip the coin 20 times for your sampl your sample of 20 coin flips all landed on heads, would it prove with complete certainty that your friend's coin is weighted