Step-by-step explanation:mean value : the sum of the measurements of all 10 plants divided by 10 (the number of measurements).A)since the 2 measurement errors are compensating each other in the sum of measurements (-5 cm vs. +5 cm), the sum stays the same, the number of measurements stays the same (10), so the mean value stays the same (72 cm).B)the mean absolute deviation was the mean value of the absolute values of the differences of each measurement to the plant measurements.since the mean value stayed the same, so did the difference of the 8 originally correct measurements to that mean value.the only change is with the 2 corrected measurements. the original (but wrong) measurement of 65 had a difference of 7 (to 72).and now it is only 2 (70 to 72).and the other one had a difference of 6 (72 to 78).and now it is only 1 (73 to 72).so, the sum of all the differences decreased by (7-2) + (6-1) = 5 + 5 = 10.we had originally a mean absolute deviation of 8.5. the sum of all 10 original differences was therefore 8.5×10 = 85.now this sum went down to 85-10 = 75.and the new mean absolute deviation is 75/10 = 7.5.