Brain Teasers
1. Palani makes and sells wooden tables from his yard for Rs. 100 each. His only costs are for materials. It takes him an hour and half to make a table. He sold 200 last year, for a profit of Rs. 3,000. This year he raises the price by 15%, but sells 30% fewer tables. Assuming his cost for making each table hasn't changed, by what percentage does his profit increase?
2. The Jail Cell Clock Riddle
You are locked in a jail cell with no windows and you need to tap out a message on the wall for the man in the other cell next to you. The problem is that you have to do it at exactly 9:15 PM, when the guard outside is switched, so your noise won't be noticed. You can't hear the switching of the guards through your walls, and you have no clock.
There is a faucet with water dripping very consistently from it in the corner, but you don't know how many drops fall per minute, and that wouldn't give you the time in any case. You can just make out the chiming of a church bell, but it chimes just once at the start of each hour, so you can't tell the time from that. Your dinner is not given to you at any exact time, but only passed into your cell between 6:15 and 6:45 PM.  How do you determine when it is exactly 9:15 PM?