Answer: 1.25
Step-by-step explanation:
Given: A college-entrance exam is designed so that scores are normally distributed with a mean = 500 and a standard deviation
= 100.
A z-score measures how many standard deviations a given measurement deviates from the mean.
Let Y be a random variable that denotes the scores in the exam.
Formula for z-score =
Z-score =
⇒ Z-score =
⇒Z-score =1.25
Therefore , the required z-score = 1.25
Answer:
The half-life of the radioactive substance is 135.9 hours.
Step-by-step explanation:
The rate of decay is proportional to the amount of the substance present at time t
This means that the amount of the substance can be modeled by the following differential equation:
Which has the following solution:
In which Q(t) is the amount after t hours, Q(0) is the initial amount and r is the decay rate.
After 6 hours the mass had decreased by 3%.
This means that . We use this to find r.
So
Determine the half-life of the radioactive substance.
This is t for which Q(t) = 0.5Q(0). So
The half-life of the radioactive substance is 135.9 hours.