10 meters, because 25 percent of 8 is 2, 2 plus 8 is 10.
The answer should be 7(x+8)
Hey ok, let me work this problem out, could u give me the formal?
i cant find the notes so i need the formal.
Answer:
4.924 years
Step-by-step explanation:
Lets denote X the lifetime of a tv tube (In years). X has distribution 
, with 
unknown.
We know that P(X < 4) = 0.2. Using this data, we can find the value of throught standarization.
Lets call 
the standarization of X. Z has distribution N(0,1), and its cummulative function, 
is tabulated. The values of can be found in the attached file.
The value q such that 
doesnt appear on the table. We can find it by using the symmetry of the normal density function. The opposite of q, -q must verify that 
, hence -q must be equal to 0.84. Thus, q = -0.84
But this value of q should match with the number 
, so we have
Thus, the expected lifetime of TV tubes is 4.924 years.
I hope this works for you!
