High School

One of the admission requirements for international students is to demonstrate English language proficiency. The TOEFL test is one of the options candidates can choose. The mean score for the TOEFL test is 88 points, and the standard deviation is 12 points. This test score follows a normal distribution.

1. What is the TOEFL score that separates the top 25% from the bottom 75%?
A. 96.0939
B. 92.6238
C. 83.3762
D. 79.9061

2. An international candidate gets a TOEFL score above the average. An education department requires a minimum TOEFL score of 108 as part of the admission requirements. Calculate the probability that this candidate meets the TOEFL score requirement by the education department. (Hint: Apply the concept of conditional probability)
A. 0.05
B. 0.048
C. 0.0956
D. 0.9522
E. 0.9044

Answer :

The TOEFL score that separates the top 25% and bottom 75% is approximately 96.1. And the probability that an international candidate who scores above average will also meet the minimum TOEFL score requirement of 108 is 0.048 or 4.78%.

Firstly, let's look at the score that separates the top 25% and the bottom 75%. This is often referred to as the 75th percentile. Since the scores follow a normal distribution, we use a standard z-score table to find the corresponding z-score for the top 25%, which is approximately 0.675. We then convert this z-score to a TOEFL score using the formula: TOEFL Score = Mean + (Z-score * Standard Deviation). Given the mean is 88 and the standard deviation is 12, our calculation becomes: TOEFL Score = 88 + (0.675 * 12), which equals around 96.1. This means option A. 96.0939 is the closest answer.

Next, let's address the second part of your question. Here, we need to calculate the probability that a candidate who scores above average will also meet the minimum TOEFL score requirement of 108 set by the education department. To do this, we need to calculate a new z-score: Z = (108 - Mean) / Standard Deviation. Plugging in our values, we get Z = (108 - 88) / 12 = 1.67. Looking up 1.67 in the z-score table, we see the area to the left is 0.9522, which means there is a 95.22% chance that a randomly chosen candidate would score less than 108. To find the probability that the candidate scores 108 or more, we subtract this from 1 (because the total probability is 1), which gives us 1 - 0.9522 = 0.0478 or 4.78%. So the answer is B. 0.048.

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