1. The figure above shows a student's production function with the final grade (the output) related to the number of hours spent studying (the input). Which of the following statements regarding marginal product of labor (MPL) are correct?
2. The MPL is decreasing beyond 15 hours of study.
3. The MPL at 4 hours is 12.5.
4. The MPL is the slope of the tangent line.
5. The MPL is always greater than the APL.

100 90 80 70 60 Final grade 50 40 30 20 10 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hours of study per day Study hours 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 or more Grade 0 20 33 42 50 57 63 69 74 78 81 84 86 88 89 90