Final answer:
The estimated amount of fat in a 20-pound weight gain by an adult is approximately 17.5 pounds.
Step-by-step explanation:
The correct answer is d. 12.5 lbs.
When an adult gains 20 pounds of body weight, it does not necessarily mean that all of it is fat. The weight gain can be a result of various factors, including muscle gain, water retention, or even bone density. However, if we assume that the weight gain is primarily due to fat accumulation, a general estimation is that 1 pound of stored body fat is equal to about 3,500 extra calories consumed (according to the provided information).
Therefore, if an adult gains 20 pounds of body weight, they have accumulated approximately 70,000 extra calories (20 pounds x 3,500 calories per pound). Dividing this by the number of calories in 1 pound of fat (4,000 calories, according to the provided information), we can estimate that about 17.5 pounds of the weight gain is fat (70,000 calories / 4,000 calories per pound = 17.5 pounds). Rounded to the nearest whole number, this is approximately 18 pounds. Since the question asks for an estimate, the closest option is d. 12.5 lbs.