Thirty By A Half
If you divide thirty by 1/2 and add 10 what would you have?
The lightbulb
There are 100 light bulbs lined up in a row in a long room. Each bulb has its own switch and is currently switched off. The room has an entry door and an exit door. There are 100 people lined up outside the entry door. Each bulb is numbered consecutively from 1 to 100. So is each person. Person No. 1 enters the room switches on every bulb and exits. Person No. 2 enters and flips the switch on every second bulb (turning off bulbs 2 4 6

