Q: Scores: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. Find P90 and D7. n = 10. P90 position = 90(11)/100 = 9.9th value: between 90 and 100. Interpolate: 90 + 0.9(10) = 99. P90 = 99. D7 = P70: position 70(11)/100 = 7.7th: between 70 and 80: 70 + 0.7(10) = 77.