A Tutor Promises to Improve GMAT Scores of Students by More

question 21

Multiple Choice

A tutor promises to improve GMAT scores of students by more than 50 points after three lessons. To see if this is true, the tutor takes a sample of 49 students' test scores after and before they received tutoring. The mean difference was 53 points better after tutoring, with a standard deviation of the difference equal to 12 points. Let µ_D denote the mean of the difference: score after tutoring minus score before tutoring. Assuming α = 0.05, which of the following is the appropriate critical value?

• A) z = 1.677
• B) z = 2.011
• C) t_0.05,48 = 1.677
• D) t_0.05,₄₈ = 2.011

---

Definitions:

Compulsive Personality

A personality trait characterized by a strong urge to perform certain actions repeatedly, often linked to obsessive-compulsive disorder.

Bone Spur

A bony growth formed on normal bone, often causing pain and discomfort when it rubs against tissues or nerves.

Gift Causa Mortis

A gift made in contemplation of imminent death, which becomes effective only if the donor dies as anticipated.

Lottery Ticket

A piece of paper or a digital token that allows the holder a chance to win a prize in a drawing of lots.