The Graduate Management Admission Test (GMAT) is a requirement for all applicants of MBA programs. A variety of preparatory courses are designed to help applicants improve their GMAT scores, which...

The Graduate Management Admission Test (GMAT) is a requirement for all applicants of MBA programs. A variety of preparatory courses are designed to help applicants improve their GMAT scores, which range from 200 to 800. Suppose that a survey of MBA students reveals that among GMAT scorers at least 650, 72% took a preparatory course; whereas among GMAT scores of less than 650 only 31% took a preparatory course. The probability for an applicant to score at least 650 is 30%. Suppose he was not taking the preparatory course. What is his probability of achieving 650 or more for GMAT score?