Coredata vs SQLite? Why NSFetchResultController is used and is it bound to a view?

Atomic vs non atomic properties.

Gcd vs nsoperationqueue

How nsdictionary internally works ( same question how HashMap works internally in java )

There are R G B colored balls of P Q R quantity simultaneously. If a person takes out 2 balls at one go what is the probability of getting 2 balls of same color in 3rd draw

There is a room with one entry one exit and n nunber of cupboards . Every cupboard is numbered from 1 to n. Every staff member is Also numbered from 1 to n. If a staff member enters the room he'll toggle(means if closed then will open else vice cersa) the cupboard if that cupboard number is divisible by his number. Aftr n staff members visit. How many cupboards will be in open state.

Put forward a algorithm to implement notifications as its present in cocoa. What are semaphores and when to use it.race condition and starving?