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(a) First calculate the number of those workers who own at least one of the items.
For it, calculate the alternate sum
560 + 560 + 275 - 350 - 220 - 160 + 150 = 815.
The rest 830 - 815 = 15 workers do not own any of the three items. ANSWER
(b) Only cars and houses 350 - 150 = 200.
Only cars and boats 160 - 150 = 10.
Only houses and boats 220 - 150 = 70.
The subsets of workers counted in the previous 3 lines are DISJOINT.
Therefore, the number of workers who own only two items is 220 + 10 + 70 = 300. ANSWER
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For more details and explanations, read the lessons
- Advanced problems on counting elements in sub-sets of a given finite set
- Challenging problems on counting elements in subsets of a given finite set
in this site, where you will find many similar solved problems.