An unknown radioactive element decays into non-radioactive substances. In 180 days the radioactivity of a sample decreases by 73
percent.
(a) What is the half-life of the element? (in days)
(b) How long will it take for a sample of 100 mg to decay to 60 mg? (in days)
(a) What is the half-life of the element? (in days)
(b) How long will it take for a sample of 100 mg to decay to 60 mg? (in days)
1 answer:
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Answer:
The minimum score required for admission is 21.9.
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 university plans to admit students whose scores are in the top 40%. What is the minimum score required for admission?
Top 40%, so at least 100-40 = 60th percentile. The 60th percentile is the value of X when Z has a pvalue of 0.6. So it is X when Z = 0.255. So
The minimum score required for admission is 21.9.