NIMCET 2013 — Reasoning PYQ

Solving:

We need to check which original setting leads to the changed state where only $B$ is $ON$ (i.e., $A=OFF,B=ON,C=OFF$).

Testing Option 2:

• Original: $A=ON,B=OFF,C=ON$.

• Rules Check:

  • Rule (i): $A$ is not the only switch $ON$ ($C$ is also $ON$).

  • Rule (ii): $A$ and $B$ are not the only switches $ON$.

  • Rule (iii): All three are not $ON$ ($B$ is $OFF$).

• Rule Application: Since rules (i), (ii), and (iii) fail, apply Rule (iv) (Invert all).

  • $A:ON\to OFF$

  • $B:OFF\to ON$

  • $C:ON\to OFF$

• Final Result: Only $B$ is $ON$.