assume that random guesses are made for 8 multiple choice questions on an SAT test, so that there are n=9 trials, each with prob
1 answer:
Answer:
Step-by-step explanation:
If we call x the number of correct questions obtained in the 9 attempts, then:
x is a discrete random variable that can be modeled by a binomial probability distribution p, with n = 9 trials.
So, the p of x successes has the following formula.
Where:
n = 9
p = 0.6
We are looking for P(x<4)
By definition:
Then:
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Answer:
a) 0.18% of cold sufferers experience fewer than 4 days of symptoms
b) 64.40% of cold sufferers experience symptoms for between 7 and 10 days.
Step-by-step explanation:
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean and standard deviation
, the zscore of a measure X is given by:
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
In this problem, we have that:
a. What proportion of cold sufferers experience fewer than 4 days of symptoms?
This is the pvalue of Z when X = 4. So
has a pvalue of 0.0018.
So 0.18% of cold sufferers experience fewer than 4 days of symptoms.
b. What proportion of cold sufferers experience symptoms for between 7 and 10 days?
This is the pvalue of Z when X = 10 subtracted by the pvalue of Z when X = 7. So
X = 10
has a pvalue of 0.9812.
X = 7
has a pvalue of 0.3372.
So 0.9812 - 0.3372 = 0.644 = 64.40% of cold sufferers experience symptoms for between 7 and 10 days.