There are 4 isosceles triangles in a rectangle:)
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
Answer:
The answer is B - 288
To get this answer all you need to do is
First, subtract 316 - 28 to get your answer :)
Hope this helps!
-sofia~
If your looking for the sum, it would be -5 :)
She would need to buy 75% of the dress Bc 100%-25% is 75%
