Happy to help! This one tripped me up for a minute too!
We know that a lighting panel has exactly seven switches which are either on (O) or off (F).
In a bit of a confusing twist, we also learn that the circuit load of the panel is the total number of switches that are O e.g. if 4 out of 7 switches are on, then the circuit load of the panel is 4.
_ _ _ _ _ _ _ 1 2 3 4 5 6 7
Rule 1 - if 1 is O, then 3 and 5 are F
1O --> 3F AND 5F 3O OR 5O --> 1F
Rule 2 - if 4 is O, then 2 and 5 are F
4O --> 2F AND 5F 2O OR 5O --> 4F
Rule 3 - the switch whose number corresponds to the circuit load of the panel is O
E.g. if the circuit load is 4, then Switch 4 must be O
The question stem tells us that Switch 5 and Switch 6 are O.
Based on the conditions above, we can deduce that Switch 1 and Switch 4 must be F. This eliminates answer choices (A) and (D).
F _ _ F O O _ 1 2 3 4 5 6 7
We have three unknowns remaining. We do not know whether Switches 2, 3, and 7 are O or F.
We do know that the switch whose number corresponds to the circuit load of the panel is on. The circuit load cannot be 6 or 7 because Switch 1 and Switch 4 are off. The circuit load also cannot be 2 because this would mean that Switch 2 would have to be O, making the circuit load 3.
Therefore, the circuit load could be either 3 or 5.
If the circuit load is 3, then Switch 3 must be O and Switches 2 and 7 must be off. This eliminates answer choices (B) and (E) because there is a possible configuration where neither Switch 2 nor Switch 7 is O.
This means that the correct answer should be 3, but let's double-check!
If the circuit load is 3, then Switch 3 must be O. If the circuit load is 5, then Switches 2, 3, and 7 must all be O. Either way, Switch 3 must be on.
Hope this helps! Please let us know if you have any further questions.
