Question

At a particular time of computation the value of a counting semaphore is 7.Then 20 P operations and 15 V operations were completed on this semaphore. The resulting value of the semaphore is? (GATE 1987)

(a) 42

(b) 2

(c) 7

(d) 12

The question was posed to me at a job interview.

The above asked question is from Semaphores topic in division Process Synchronization of Operating System

Answer 1

Right option is (b) 2

To explain: P represents Wait and V represents Signal. P operation will decrease the value by 1 every time and V operation will increase the value by 1 every time.