19. A large computer system has 100 identical components which are subject to random failure over time.

The failure pattern is given as follows:

Failed components have to be replaced immediately for the effective functioning of the computer. If they are replaced individually, as and when they fail, then the cost per replacement is estimated as Rs 4. Alternatively, if all the components are replaced in one lot at periodical intervals, then the cost per unit is estimated as Rs 1.50.
(i) Determine the more economical of the two policies of complete individual replacement or periodic group replacement.
(ii) Would the above decision remain valid if the unit cost in group replacement is given to be Rs 2?
Justify your answer.

Month end 1 2 3 Failure to date (percentage) 12 28 50 45 5 6 75 90 90 100