Question

. A shipyard makes a container ship that can withstand the total amount of weight W, which is normally distributed with mean of 600 tons and standard deviation of 60 tons. Let us assume that the weight of a single container that will be loaded to the container ship is also normally distributed with mean of 4 tons and standard deviation of 0.4 tons. What is the maximum number of containers that the ship can load and still have at least a 90% chance to not exceed its weight limit

Answer 1

Answer:

the maximum number of containers that the ship can load is 170

Step-by-step explanation:

Given the data in the question;

W ~ N( 600, 60 )

S ~ N( 4n, 0.4√n )

so

p( W > S ) = 0.90

⇒ P( W - S > 0) = 0.9 ------ let this be equation 1

now, since W and S are independent

Mean( W - S ) = Mean( W ) - Mean( S 0 = 600 - 4n

and

SD( W - S ) = √( var(W) + var(S) ) = √( 60² + 0.4²n)

hence;

W - S ~ N( 600 - 4n, √( 60² + 0.4²n) )

now, from equation one, P( W - S > 0) = 0.9

$P( \frac{(W-S)-Mean(W-S)}{SD(W-S)} > \frac{0-(600-4n)}{\sqrt{60^2 + 0.4^2n} }) = 0.90$

$P( z > \frac{0-(600-4n)}{\sqrt{60^2 + 0.4^2n} }) = 0.90$

from z- table

$P( z > \frac{0-(600-4n)}{\sqrt{60^2 + 0.4^2n} }) = P( z >-1.282)$  

$\frac{4n - 600}{\sqrt{60^2 + 0.4^2n} } = -1.282$ ------------------ let this be equation 2

now, we square both sides of equation 2

$\frac{(4n - 600)^2}{60^2 + 0.4^2n} } = (-1.282)^2$  

$\frac{(4n - 600)(4n-600)}{3600 + 0.16n} } = 1.643524$

we cross multiply

16n² + 360000 - 4800n = 1.643524( 3600 + 0.16n )

16n² + 360000 - 4800n = 5916.6864 + 0.26296384n

16n² + 360000 - 5916.6864 - 4800n - 0.26296384n = 0

16n² + 354083.3136 - 4800.26296384n = 0    

16n² - 4800.26296384n + 354083.3136 = 0  

solving the quadratic equation, we know that;

x = -b±√( b² - 4ac ) / 2a

so we substitute

x = [-(-4800.26296384) ±√( (-4800.26296384)² - (4 × 16 × 354083.3136)] / [2×16]

x = [ 4800.26296384 ±√( 23042524.522 - 22661332.0704 ] / 32

x = [ 4800.26296384 ±√(381192.4516) ] / 32

x = [ 4800.26296384 ± 617.4078 ] / 32

Hence;

x = [ 4800.26296384 - 617.4078 ] / 32 or  [ 4800.26296384 + 617.4078 ] / 32

x = 131   or  170

Therefore, the maximum number of containers that the ship can load is 170