Double Negatives: Is Kaplan PSAT Math Book Wrong?

[Qube]

Hi guys. I was reading a Kaplan PSAT book which is required for my school. I have a little math question that needs to be cleared up.

I stumbled across this (below) and I'm 99% sure the book is wrong. I took a screenshot of it using Google Books.

Am I wrong, or is the book wrong?

http://i.min.us/ibx49LSbJ.png

 

[Dembadon]

Hi guys. I was reading a Kaplan PSAT book which is required for my school. I have a little math question that needs to be cleared up.

I stumbled across this (below) and I'm 99% sure the book is wrong. I took a screenshot of it using Google Books.

Am I wrong, or is the book wrong?

http://i.min.us/ibx49LSbJ.png

The book is wrong.

 

[cepheid]

To elaborate, adding two negatives together doesn't make a positive. Multiplying two negatives together makes a positive. In other words, if you negate a negative number, you end up with a positive one (because the way to negate something is to multiply it by -1). This is the analogy the the book was trying (but failed) to make. In English it is similar: if you negate a statement that is already phrased as a negative, then the two cancel each other out. E.g. "I ain't got no money," which in correct English would be, "I haven't got no money." But if you haven't got no money, then you must have some money. So you can see that the meaning of the sentence with the double negative is the same as the meaning of the sentence, "I have got some money." So, double negatives are deemed incorrect in English (i.e. shouldn't be used) because there are only two possible intended uses:

1. An incorrect way of phrasing something as a negative

2. A confusing and unnecessarily convoluted way of phrasing something as an affirmative.

 

[Qube]

Thanks guys for debunking this math screw-up :).

 

[256bits]

To elaborate, adding two negatives together doesn't make a positive. Multiplying two negatives together makes a positive. In other words, if you negate a negative number, you end up with a positive one (because the way to negate something is to multiply it by -1). This is the analogy the the book was trying (but failed) to make. In English it is similar: if you negate a statement that is already phrased as a negative, then the two cancel each other out. E.g. "I ain't got no money," which in correct English would be, "I haven't got no money." But if you haven't got no money, then you must have some money. So you can see that the meaning of the sentence with the double negative is the same as the meaning of the sentence, "I have got some money." So, double negatives are deemed incorrect in English (i.e. shouldn't be used) because there are only two possible intended uses:

1. An incorrect way of phrasing something as a negative

2. A confusing and unnecessarily convoluted way of phrasing something as an affirmative.

Cepeid gave good explanation but to add,
For those learning to be puritans of English:
E.g. "I ain't got no money,"
"ain't got " - ain't is not an (acceptable) word in proper English.

And the "got" is poor colloquial spoken English, and should be eliminated.
"I have got some money " --> "I have some money".


Intended use number 3.
Double negatives are used in English to also provide emphasis to certain thoughts or ideas, that without, lacks what a speaker or writer wishes to convey. At times the double negatives do not cancel out as one wishes to think.

A simple example
"That cat will never not stop scratching my furnature!" <-- emphasis
Means the same as " "That cat will never stop scratching my furnature!" <-- booring
or "That cat will not stop scratching my furnature!" < - booring

BUT it does not mean
""That cat will stop scratching my furnature!" <- double negaive elimination

 

[Mark44]

Intended use number 3.
Double negatives are used in English to also provide emphasis to certain thoughts or ideas, that without, lacks what a speaker or writer wishes to convey. At times the double negatives do not cancel out as one wishes to think.

A simple example
"That cat will never not stop scratching my furnature!" <-- emphasis

Do you have any examples of anyone actually talking or writing like this?

Means the same as " "That cat will never stop scratching my furnature!" <-- booring
or "That cat will not stop scratching my furnature!" < - booring

BUT it does not mean
""That cat will stop scratching my furnature!" <- double negaive elimination

IMO, cepheid pretty well covered things with his two examples. I'm not sure what you're trying to convey with your "simple" example.