Calculating Frequencies A frequency is written as the number of times an event occurs divided by the number of times the event could have occurred. If you flipped a coin 10 times and got 6 heads and 4 tails, then the frequency of heads was 6/10. It is typically written as fheads) - 6/10 or 0.6. For our purposes, an expected frequency is defined as the proportion of times an event should occur based on what you know about the event. For example, heads and tails are found on opposite sides of a coin, so each event (getting a head or getting a tail) should occur 50% of the time if the flips are random events. Thus the expected frequency of heads is 5/10 or 0.5. We can compare the expected frequency to the observed frequency and see if they match. In this case, the observed frequency (0.6) does not match the expected frequency (0.5). Does this mean that the coin flipper was cheating?