This is a question from April 2018 QAS, Calculator Section, Problem 29.

I can’t figure out why choice D is the correct answer. I was stuck bw choice A and B, and picked A. Why is A wrong and D correct?

Thank you!

Hello Mike,
Basically, I’m having a little trouble understanding the explanation for #3 on the Working in Three Dimensions section on page 284. I got a little lost after the part where you explained how d was the height (this makes sense to me). Like, how do we “recognize that the ab term in the surface area expression must represent both the top and the bottom of the prism”? I think it’s somewhere from the equation but I don’t know where. I would greatly appreciate your help here Mike. Thanks!

Hello Mike,
For problem 2 on page 284 (relating to “Working in Three Dimensions”), I had difficulty answering the question, because I don’t know what the inner radius of a sphere and how that differs from the outer radius of a sphere. Since I’m not able to find anything on the Internet that talks about this, could you please explain the difference to me?
And could you then tie it back to how the entire inner/outer radius thing is relevant to the question at hand (#2 on page 284)?