Final answer:
The average growth rate of fingernails in a normal adult is about 0.1 mm per day or 3 mm per month. This equates to roughly 0.5 mm per week. To achieve record lengths such as those documented in Guinness World Records would take multiple centuries of growth.
Step-by-step explanation:
The average rate of growth of fingernails in a normal adult is approximately 3 mm per month. This means that fingernails grow at about 0.1 mm per day, which would be option b, 0.5 mm per week if we're discussing a weekly rate, not daily. Fingernails grow continuously throughout our lives from the nail matrix, a layer of living epidermal tissues. Factors such as age, sex, and season can affect the growth rate, making it faster or slower. However, the given rate is an average. Given that the current record-holder for the longest fingernails for women has nails totaling 28 feet for all nails, and assuming a consistent growth rate, it would take many years to achieve such lengths. Specifically, to grow a single fingernail to a length of 2 feet 11 inches, assuming no breakage or trimming, it would require more than 224 years of continuous growth at the rate of 3 mm per month.