Question

Here are the science test scores from Ms. O’Donnell’s class:

55, 60, 70, 70, 75, 75, 75, 80, 80, 85, 85, 85, 85, 90, 90, 95, 100

Find the mean absolute deviation (MAD).

Answer 1

Step 1 — mean:
Sum = 1355, n = 17, mean = 1355/17 ≈ 79.705882.

Step 2 — sum of absolute deviations:
Sum |x − mean| = 155.88235295 = 2650/17.

Step 3 — MAD:
MAD = (1/17)·(sum |x − mean|) = 2650/289 ≈ 9.16955.

So the mean absolute deviation ≈ 9.17.