ITPEC IP October 2022 Question 2
ITPEC IP October 2022 — Question 2 of 100
There are 26 patterns with at least two lamps on. Five independent on/off lamps have 2⁵ = 32 total patterns. Exclude the one pattern with no lamps on and the five patterns with exactly one lamp on: 32 − 1 − 5 = 26.
Answer (c)
Why not others:
- 4 and 10 count only limited selections
- 32 includes the zero-lamp and one-lamp patterns that the condition excludes
Key rule: Count all binary patterns, then subtract the disallowed cases; equivalently sum the combinations for choosing 2, 3, 4, or 5 lamps.
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