Classic Mind-benders

1 kilo of cotton and 1 kilo of iron — Sohan thinks iron is heavy, so 1 kilo of iron will weigh more than 1 kilo of cotton. His sister says both weigh the same. Who is right?

The question is: "How many months of the year have 28 days?" Maansi quickly answers "only February", thinking the question is asking which month ends at exactly 28 days. Her brother says reading the question carefully gives a different answer. Who is right?

A "magic" trick: think of any number, double it, add 10, halve it, then subtract the starting number — the answer is always 5. Kartik thinks this only works for small numbers. His sister says it works for every number, however large. Who is right?

Outside a room are 3 switches, each controlling one of 3 old-style bulbs inside the room (which get hot when lit). You can enter the room only once. Divya thinks that without going in repeatedly, it is impossible to figure out which switch controls which bulb. Her friend says there is a way. Who is right?