概率统计计算
In a study of 85 third year students,it was found that 30 of them had a job (usually part time),33 had achieved a credit level in the previous year,and 23 had a job AND had achieved a credit level in the previous year.Using a contingency table or otherwise,answer the following questions.
Find the probability that a student,chosen at random from those who achieved credit level,had a job.