The probability that at least one of the calculators is defective is : 0.725
<h3>What is probability?</h3>
Probability is the likelihood of an event happening or not.
if there is certainty that the event would happen probability is 1.
Analysis:
probability = required outcome/possible outcome
for 33 good calculators and 12 defective calculators, total calculators = 45
4 calculators were chosen, possible outcome = 45C4 = 148995
Required outcome = 33C3 . 12C1 + 33C2 . 12C2 + 33C1 . 12C3 + 33C0 . 12C4
= 65472 + 34848 + 7260 + 495 = 108075
Probability = 108075/148995 = 0.725
Learn more about Probability: brainly.com/question/25870256
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For some value of z, the value of the cumulative standardized normal distribution is 0.8340. the value of z is
Answer: We are required to find the value of z corresponding to probability 0.8340.
i.e., 
We can find the value of z using the standard normal table.
Using the standard normal table, we have:

Therefore, for the value of z = 0.97, cumulative standardized normal distribution is 0.8340
Attached here standard normal table for your reference.
I’m pretty sure you can just do 1/2! since B is 0.75 and A is 0.25 so 0.75-0.25=0.5=1/2