Let
be the random variable for the number of marks a given student receives on the exam.
10% of students obtain more than 75 marks, so

where
follows a standard normal distribution. The critical value for an upper-tail probability of 10% is

where
denotes the CDF of
, and
denotes the inverse CDF. We have

Similarly, because 20% of students obtain less than 40 marks, we have

so that

Then
are such that


and we find

after 4 days 88 boats will have passes under the bridge
The answer is between 45,000,000-65,000,000
Answer: The answer is 34,000 cm
Step-by-step explanation: I just did that
Answer: The answer is -30 - 45 k
Step-by-step explanation: