Please help me with this Physics problem. I don't understand how to set it up. (problem post in the Q)

Question

anonymous · Answer

THE PROBLEM:

You$\tiny~~$hire$\tiny~~$a$\tiny~~$printer$\tiny~~$to$\tiny~~$print$\tiny~~$concert$\tiny~~$tickets.$\tiny~~~$He
delivers$\tiny~~$them$\tiny~~$in$\tiny~~$circular$\tiny~~$rolls$\tiny~~$labeled$\tiny~~$as 1000
tickets each.$\tiny~~$You want to check the number of
tickets in each roll without counting thousands
of$\tiny~~$tickets.$\tiny~~$You$\tiny~~$decide$\tiny~~$to$\tiny~~$do$\tiny~~$this by measuring
the$\tiny~~$diameter$\tiny~~$of$\tiny~~$the$\tiny~~$rolls.$\tiny~~~$The$\tiny~~$tickets$\tiny~~$are$\tiny~~~$3$\tiny~~$in
long$\tiny~~$and$\tiny~~$0.25$\tiny~~$mm$\tiny~~~$thick$\tiny~~~$and$\tiny~~~$are$\tiny~~~$rolled$\tiny~~~$on$\tiny~~~$a
core 4 cm in diameter.

farcher · Answer

What volume would you expect the tickets to have?
What is the volume of the roll which is a hollow cylinder?
Compare the two volumes.

anonymous · Answer

I forgot the question:
`What should be the diameter of a roll of 1000 tickets? `

The volume of each ticket is:
0.25 mm * 3 inches = 19 mm²

And the volume of 1000 tickets is:
19,000 mm²

farcher · Answer

So you call the outer radius R find the volume of the roll in terms of the inner and outer radius = pi (R^2 - 20^2) noting that the inner diameter is 4 cm which gives a radius of 20 mm.

You can find R^2 and then R and then double it to get the diameter in mm.

You are not told the width of the tickets but that does not matter as the width will cancel out.