Answer:
4/9 or 0.4
Step-by-step explanation:
Given that normally distributed data set has a mean of 55 and 99.7% of data fall between 47.5 and 62.5.
Let s be the standard deviation of data set.
Since 99.7% data fall within 3 standard deviations of mean, z-value for 47.5 and 62.5 has an absolute value of 3.
That is |z|=3
But z= 
Let us plugin x=47.5 and mean =55 and equate it to 3.
That is 

Since x is always positive ( being standard deviation), 
Hence 

We will get same value with 62.5 as well.
Hence standard deviation of data set is 2.5.
Answer:
28:16
Total of students is 28 and 16 boys
Answer:
y=x^2-2
Step-by-step explanation:
this equation is not a linear function because the equation is that of a quadratic function
So we use 80% to multiply 20,000
we get 16000
the answer is just 16,000