- A20
- B56
- C10
- D35
Step-by-Step Solution
The 5 unlit lamps make 6 gaps (ends included). Put each lit lamp in a different gap: ignores the rule.)
Answer: A) 20
Eight lamps stand in a row. Exactly 3 are to be switched on so that no two lit lamps are next to each other. In how many ways can this be done?
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