How to boil an egg - statistics to the rescue
Large or extra-large eggs will take longer to cook than those classified as small or medium. You might, for example, typically cook a large egg in a pan of boiling salted water for seven minutes. Even if you do this and apply exactly the same amount of heat to the pan the results will not always be the same. Sometimes you will find the egg harder than you like it while on other occasions it will be too soft. The reason for this is straightforward: there can be quite a bit of variation in size and weight within a category such as ”large”.
For example the pack of nine eggs that I bought from the local co-op yesterday contained eggs varying in weight from 66 grams to 74 grams, with a mean between 69 and 70 grams and a standard deviation of about 2.5 grams. (Even these figures are not entirely accurate as my kitchen weighing machine only registers the nearest whole number of grams.)
Suppose you find that an egg weighing 70 grams was exactly as you like it when cooked for 7 minutes. This means that you should allow 1 minute for every 10 grams. In accordance with this you will get improved results if you weigh each egg before cooking and adjust the time in the pan appropriately. So a 65 gram egg should be cooked for six and a half minutes while a 75 gram egg would need seven and a half minutes. Timings for other weight eggs should be suitably adjusted. This approach should give you a perfect boiled egg every time!