Assuming Elizabeth is not gaining or losing weight from any factors other than exercise, she would lose 600 calories per session of exercise.
If she exercises regularly, let's say 3 times per week, that would be 600 calories x 3 = 1800 calories per week.
In a month (assuming 4 weeks), she would lose 1800 calories x 4 = 7200 calories.
In 16 months, she would lose 7200 calories x 16 = 115,200 calories.
To convert calories to weight, 1 pound is approximately equal to 3500 calories.
Therefore, Elizabeth would lose 115,200 calories / 3500 = 32.914 pounds.
Starting with a weight of 120 pounds, she would weigh 120 - 32.914 = <<120-32.914=87.086>>87.086 pounds in 16 months. Answer: \boxed{87.086}.
Elizabeth weighs 120 pounds. When she exercises she uses weights to gain muscle and she loses 600 calories per session of exercise. How much will she weigh in 16 months?
1 answer