Two ropes take 1h each to burn completely, yet the burning process is not uniform (Ex. 30min does not mean the fire is in the middle). How would you measure 45min?
There are 10 bags with 100 identical coins. In all bags but one, each coin weights 10g. However, all the coins in the counterfeit bag weighs 9g or 11g. Find the counterfeit bag using 1 usage of a digital scale that tells you exact weight.
I have keys but no locks. I have space but no room. You can enter, but you can't go outside. What am I?