Blink-Free Photos, Guaranteed? Fill in the blanks! In a simplified situation where the camera's shutter stays open almost instantaneously, let x = number of blinks per second and f = time during which a blink can spoil a photo. Since the time between blinks is longer than the time in which a photo can be spoilt, Le. = > t, Dr. Piers Barnes declared the chance of one blinking (thus spoiling photo) = xt AI Write down the probability of one not blinking (thus not spoiling photo) in terms of x and t. Z The average human blink lasts 0.3 second. A person being photographed blinks an average of 10 times/minute. Find the chance of one not blinking (thus not spoiling photo). For a group of 20 people, write down the probability of all not blinking (thus making a good photo). An alternate but divergent solution goes like this. Since our eyes are blinking 5% of the time, at any instant, there will be an average of blink(s) per instant for a group of 20 people taking a photograph together. Since the average blink is not dependent on your other blinks, is not dependent on someone else's blinks, and is taken as naturally random, we might model the number of blinks at a particular instant using the distribution. If plotted, a chart of the number of blinks happening in a photo of 20 people would appear in shape. Now, for a good photo to be had, no one must blink. The chance that this happens is to four significant figures. From this chance and A, the photographer would have to take at least (to the nearest rounded-up integer) photos before expecting one to contain no blinkers. And when they modelled the numbers in a chart, they saw an almost linear relationship for fewer than 20 people. Use it to complete their conclusion. ... we boiled the answer down to a very simple rule of thumb. For groups of fewer than 20 people, if you take the Number of Photos Required for 95%% Confidence number of people in the group and divide that number by | two / three / four then you should take that number of photos for one of them to be blink-free." Number of People In Group