We want 85% of the calls to be answered within the new time specification, so we must first find the the z-score z

_{0}such that P(z≤z_{0})=0.85. From a table or using a calculator you find z_{0}=1.036. Now usez = (x-µ)/σ

to find the corresponding wait time:

1.036 = (x-210)/40,

which gives x=251.45 s.

Therefore, 85% of calls should be answered within a maximum wait time of 251.45 s.

## Comments

belowa new time specification. In that case, we have P(z≤z_{0})=0.85, giving z_{0}=1.036 and x=251.45 s.