Finding the the area of the surface at one end of the steel

[chriscarson]

Homework Statement

Finding the the area of the surface at one end of the steel

Relevant Equations

pi r 2

Is there any mistake in the following answer because I m always getting the result of 10362 mm 2 ?

A piece of steel tube, has an external diameter of 140mm and an internal diameter of 80mm. What is the area of the surface at one end of the steel?
Answer (13424 mm2)

 

[haruspex]

Homework Statement:: Finding the the area of the surface at one end of the steel
Homework Equations:: pi r 2

Is there any mistake in the following answer because I m always getting the result of 10362 mm 2 ?

A piece of steel tube, has an external diameter of 140mm and an internal diameter of 80mm. What is the area of the surface at one end of the steel?
Answer (13424 mm2)

I get 10367.

 

[chriscarson]

So definitely we are right the answer is wrong .
Thanks

 

[haruspex]

I tried reversing their answer by dividing by pi. I got 4272.99..., suggesting strongly they had 4273 at some point, but that is prime!

 

[chriscarson]

I tried reversing their answer by dividing by pi. I got 4272.99..., suggesting strongly they had 4273 at some point, but that is prime!

I don t know how to reversing but it happens often that there is mistakes . At least in my class.

 

[chriscarson]

A piece of acrylic will be accurately cut to size on a laser cutter.
a. Calculate area A. (90000 mm2
)
b. Calculate area B. (360000 mm2
)
c. What is the final area A of the piece, once the centre piece B is removed?
(270000 mm2
)
Also in this one I am suspecting that question c is not making sense but I am not sure . Those in brackets are the answers.

 

[Mark44]

A piece of acrylic will be accurately cut to size on a laser cutter.
a. Calculate area A. (90000 mm2
)
b. Calculate area B. (360000 mm2
)
c. What is the final area A of the piece, once the centre piece B is removed?
(270000 mm2
)

Also in this one I am suspecting that question c is not making sense but I am not sure . Those in brackets are the answers.

The problem statement seems to be incomplete, as areas A and B aren't shown. How can one calculate the area without knowing the shape of the piece of acrylic? Is there a drawing of the shapes involved?

Since this is a new question, please start a new thread. Also, see if you can come up with a more informative thread title than "AREA".

 

[berkeman]

(Note: Thread title updated from "AREA" to a more descriptive title)