In going through A. Albert Klaf’s Calculus Refresher, republished by Dover, I came across a mistake in Appendix A. The answer to question 7 on page 88 is incorrect. The question is:

7. What are the most economical dimensions of a right circular cylindrical tank made of steel of uniform thickness and of fixed volume = 6,000 cu. ft.?

And the answer given in Appendix A, p377 is:

7. r = h = 12.41 ft

However, that would give:

V = 6004.3392

dA/dr = 78.0307

I believe the correct answer is:

r = 9.8475

h = 19.6949

giving

A = 1827.8966

If you notice any other errors in this book, let me know in the comments.