Given maximum demand for 3 process at peak
P1 = 4, P2 = 6, P3 = 8
Suppose in question no extra information is given, or no restriction is given, Then
Minimum resource require to ensure system is deadlock free = (3 + 5 + 7) + 1 = 16
But in question they have put a restriction, that maximum requirement for combination P1 and P3 are 9. So possible combination in which P1 and P3 could demand for 9 resources ( 4, 5) ( 3, 6) (2, 7) (1, 8)
Case 1 : P1 and P3 demands are (4, 5), Minumum resource require : (3 + 5 + 4) + 1 = 13
Case 2 : P1 and P3 demands are (3, 6), Minimum resource require : (2 + 5 + 5) + 1 = 13
Case 3 : P1 and P3 demands are (1,8), Minimum resource require : (0 + 5 + 7) + 1 = 13
So, in all cases minimum resource requirement as 13, therefore 13 should be correct answer.
