5lb online questions.

[bultmagl]

I have two questions. Both are related to practice problems in the online section for the 5lb. book.

1. For the purposes of the GRE are imaginary numbers considered undefined?

The problem is:

If f(x) = sqrt(x-2) / x for all integer values of x, for how many values of x is f(x) undefined?

My answer was 1. Since 0 is the only place where the function is undefined. The function lies on the imaginary axis for x<2
The solution by Manhattan was >3 (infinite).


2. I have a problem with the solution to the following problem. Is this something I'll see on the test? The second problem is a quantitative comparison as follows:

A machine shop can manufacture either 17 crankshafts or 30 gears in 10 hours of production time, but not both. Crankshafts sell for $190 apiece and gears sell for $100 apiece.

A = The value of the inventory produced by the machine shop in 270 minutes of producing crankshafts
B = The value of the inventory produced by the machine shop in 285 minutes of producing gears

My solution: crankshafts come out at 1.7/hr and gears 3/hr. 270min = 4.5 hr. Therefore the factory can produce 1.7*4.5 crankshafts = 7.65 crankshafts.
However, one cannot sell 0.65 crankshaft and it has no inherent worth until complete. Therefore, A = 7*$190 = $1330

Gears -> (285/60)*3 = 14.25. B = 14*100 = $1400

So, B > A.

Maybe this is a philosophy difference between me and the question writer.

The solution on the site says A because they sell 0.65 crankshafts and 0.25 gears somehow.

[tommywallach]

1. There is no such thing as an imaginary axis. If it doesn't give you a real number answer, it's undefined.

2. This is an incorrectly written question. Is it ours? I hope not. Wherever it came from is crazy-go-nuts.

-t

[bultmagl]

1. There is such a thing as the imaginary axis. It's located in the complex plane. The Euler Identity is incredibly important in mathematics and engineering. But, you've answered my question as it relates to the GRE, sqrt(-1) = undefined, sqrt(-1) != i.

2. The material from question 2 is from the online section of material for the 5# book 2ed. It's CH16 Q3.