Let the four numbers be \(a, b, c, d\). - Mean of the four numbers = 5 → a + b + c + d = 20 - Mean deviation of the four numbers = 3 Mean deviation = \(\frac{|a-5| + |b-5| + |c-5| + |d-5|}{4} = 3\) → Sum of absolute deviations = 12 - Mean deviation of the first three numbers a, b, c = 2 → \(\frac{|a-5| + |b-5| + |c-5|}{3} = 2\) → Sum of absolute deviations for first three = 6 - Therefore, absolute deviation for the fourth number: |d - 5| = 12 - 6 = 6 The fourth number = 6 + 5 = 11.