A telemarketing supervisor is inspecting the duration of outgoing calls made by his telemarketer. Base on past results, the average length of an outgoing telephone call from a telemarketer has been 168 seconds.

The supervisor wishes to check whether that average has decreased after the introduction of a new policy.

Based on a random sample of 100 telephone calls, he found it produced a mean of 133 seconds. He performed a relevant test at a 1% level of significance with a standard deviation of 35 seconds. Determine the probability that his test will conclude the average duration is not more than 168 seconds when actual average duration is 153 seconds.