a number of

In an exercise we were working on in class, a sentence began with A number of students. This caused confusion because a number indicates one, so it would seem that the verb should be has. However, the correct answer is A number of students have. The reason the plural verb form is used is that a number of is an idiom. The idiom, a number of, means several. With this in mind, we can go back to our sentence

A number of students (has, have) problems with pronunciation.

and substitute several for a number of.

Several students (has, have) problems with pronunciation.

With several, it is clearer that the correct verb choice is have.

Several students have problems with pronunciation.

A number of students have problems with pronunciation.

Like/As if

Here is a very helpful post from Triangle Grammar Guide on the use of like and as if:

Write as if you know what you are doing

"Like" is a preposition and should not be used at the beginning of a clause. Here is an example I encountered in my editing recently: The two friends look like they’d be more at home knocking the stuffing out of people on a football field. I changed that "like" to "as if." I seem to do that a lot, so it occurs to me that writers either don't know the correct usage or are deliberately ignoring it in favor of "conversational" writing.

John Bremner in "Words on Words" has a clear rule for determining whether to use "like" or "as/as if." Remember that "like" means "similar to" or "similarly to." Substitute "similar to" in the sentence above: The two friends look similar to they’d be more at home knocking the stuffing out of people on a football field. You can see that how wrong that is or hear how incorrect it sounds.

The post clears up for me the difference between like and as if in a way that helps me understand how the words differ in use.

Noun adjuncts

Even an old dog can learn something new.

I have taught for years that the noun coming before another noun and describing the second noun is simply a noun acting as an adjective. But there is a name for this noun. It is a noun adjunct.
Here is what I am talking about.

In the phrase raisin bread, the word raisin is a noun adjunct. It is a noun describing a second noun, bread.

This differs from a compound noun like toothbrush which is two nouns combined to form one word.

Although noun adjuncts will not be on any tests that I give, it is nice to learn something new. By the way, I checked my old grammar books, and there is nothing in them about noun adjuncts, so I guess I have an excuse for my ignorance.