How to you find degrees of freedom (z-table)?

this is my problem for stats: a disk manufacturer wishes to know the fraction of disks his companies makes which are defective. suppose a sample of 1527 floppy disks is drawn and of those 122 were defective. Construct an 85% confidence interval for the population proportion of disks which are... show more this is my problem for stats:

a disk manufacturer wishes to know the fraction of disks his companies makes which are defective.

suppose a sample of 1527 floppy disks is drawn and of those 122 were defective. Construct an 85% confidence interval for the population proportion of disks which are defective

oh and the proportion = ,080
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