Question

Given the figure below, how much paper is needed to make the drinking cup to the nearest square inch?

Answer 1

To find this, we need to find the Surface area of the lateral surface of the cone (without the circle base). 
$LSA _{cone} = \pi rl$
Now we just need to plug what we know into the equation
$r=1.5 \\l=4$
$LSA _{cone} = \pi (1.5)(4) \\LSA_{cone}= 6\pi$
Wither you can keep your answer in pi or take it out of pi, depending on what the requirements are. 
To take it out of pi you need to multiply 6 by pi (remembering to use 3.14 as pi in most cases since that is what is generally accepted on tests and exams). 
$6 \pi = 6(3.14)= 18.84$
Then rounding to the nearest square inch which would mean that the amount of paper needed is =19in²