Question 1178894
.
compressair company provides cylindrical tanks of compressed air for divers. 
There standard tank is a cylinder with a volume of 0.015 m^3. 
Each cylinder is 75cm long and is designed to fit into a special diver's pack.
a) what is the diameter of the cylinder, to the nearest centimetre
b) compressair staff are designing a new cylinder that also has a volume of 0.015 m^3, 
but uses less material to make. What are the dimensions of the new cylinder, 
to the nearest tenth of a centimetre? What is the surface area, to the nearest square centimetre?
c)compressair plans to ship 20 of its standard 75-cm-long cylinders upright 
in a closed rectangular reinforced cardboard box. Staff are considering packing 
the cylinders in identical rows or in staggered rows, as shown below. 
Which packing arrangement will require the box of least volume and surface area

box a: identical 5 on the top 4 going down
box b: staggered 5 on the top 4 going down  
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First,  nothing is shown below.


Second,  part  (c)  of this problem looks like a  JOKE  or a  TRAP.


                Why did I say it ?


Because the scheme   5 + 4 + 5 + 4   allows packing only  5 + 4 + 5 + 4 = 18 cylinders,
and  2  cylinders of  20  remain unpacked.


So,  EITHER  the problem formulation is skew and curved  OR  the solution in the post by @CPhill is incorrect.



Thank you for making me smiling !