Infant stage

Old age

Youth

In all the above

Group replacement

Individual replacement

Repair spare replacement

Successive replacement

$\mathrm{m}\times \mathrm{n}$

$\left(\frac{\mathrm{m}}{\mathrm{n}}\right)-1$

$\mathrm{m}+\mathrm{n}+1$

$\mathrm{m}+\mathrm{n}-1$

In its infant state

When a machine is an old one

Scrapped

None of these

Operate up to failure and do corrective maintenance

Reconditioning

Replacement

Scheduled preventive maintenance

When money value does not change with time and time is a continuous variable

When money value changes with time

When money value does not change with time and time is a discrete variable

Preventive maintenance policy

Is not equal to the current running cost

till the current period is greater than that of next period

of the current period is greater than that of the next period,

of the current period is less than that of next period

infant

youth

old age

any time in its life

Random failure

Early failure

Chance failure

Wear - out failure

When large number of identical items is to be replaced

Low cost items are to be replaced, where record keeping is a problem

For items that fail completely

Repairable items