Numerical Problems II: Number of Elements in a Set (Three Sets)
NP1: A research team interviewed 100 people and recorded their status regarding three conditions: I = Idle P = Poor W = Willing to work The results were as follows: Category Number of People Idle (I) 28 Poor (P) 33 Willing to work (W) 14 Idle and Poor (I ∩ P) 12 Idle and Willing to work (I ∩ W) 9 Poor and Willing to work (P ∩ W) 6 Idle, Poor, and Willing (I ∩ P ∩ W) 5 1. Check whether the data are consistent. 2. Find how many people are either idle, poor, or willing to work, n(I ∪ P ∪ W). Solution : We use the inclusion-exclusion principle for 3 sets: n(I ∪ P ∪ W) = n(I) + n(P) + n(W) − n(I ∩ P) − n(I ∩ W) − n(P ∩ W) + n(I ∩ P ∩ W) n(I ∪ P ∪ W) = 28 + 33 + 14 − 12 − 9 − 6 + 5 n(I ∪ P ∪ W) = 75 − 27 + 5=53 n(I ∪ P ∪ W) = 53 So, only 53 people are in I ∪ P ∪ W. That means: People not in any group, n(I' ∩ P' ∩ W') = 100 − 53 = 47 ∵ The union count is ≤ 100 and all overlaps are consistent with the in...