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levacccp [35]
3 years ago
5

A toxic radioactive substance with a density of 7 milligrams per square centimeter is detected in the ventilating ducts of a nuc

lear processing building that was used 45 years ago. If the half-life is 20 years, what was the density of the substance when it was deposited 45 years ago?
Mathematics
1 answer:
uysha [10]3 years ago
5 0
For this case we have an equation of the form:
 y = A * (b) ^ t
 Where,
 A: initial amount
 b: decrease rate
 t: time in years.
 Substituting values we have:
 7 = A * (0.5) ^ ((1/20) * t)
 For t = 45 years we have:
 7 = A * (0.5) ^ ((1/20) * 45) 
 Clearing A:
 A = 7 / ((0.5) ^ ((1/20) * 45))
 A = 33.3
 Answer:
 
the density of the substance when it was deposited 45 years ago was:
 
A = 33.3 milligrams per square centimeter
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Answer:

The designed life should be of 21,840 vehicle miles.

Step-by-step explanation:

Normal Probability Distribution

Problems of normal distributions can be solved using the z-score formula.

In a set with mean \mu and standard deviation \sigma, the z-score of a measure X is given by:

Z = \frac{X - \mu}{\sigma}

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 p-value, we get the probability that the value of the measure is greater than X.

Mean of 35,000 vehicle miles and a standard deviation of 7,000 vehicle miles.

This means that \mu = 35000, \sigma = 7000

Find its designed life if a .97 reliability is desired.

The designed life should be the 100 - 97 = 3rd percentile(we want only 3% of the vehicles to fail within this time), which is X when Z has a p-value of 0.03, so X when Z = -1.88.

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3 0
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<em>Thus, the dimensions of the metal plate are 10 dm and 8 dm.</em>

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