Final answer:
The outcome of Liz flipping a fair coin 30 times and getting 21 heads and 9 tails is within the expected range of variability. As the number of coin flips increases, the percentage of heads and tails will tend to approach 50 percent each.
Step-by-step explanation:
When you flip a fair coin, the probability of it landing on heads is 0.5 and the probability of it landing on tails is also 0.5. In this case, Liz flipped the coin 30 times and observed that it landed heads up 21 times and tails up 9 times. While this outcome seems to favor heads, it is within the range of expected variability when flipping a fair coin. The law of large numbers states that as the number of coin flips increases, the percentage of heads and tails will tend to approach 50 percent each.