3. I got 100 on the test.

3-1. I got a 100 on the test.
3-2. I got a 100 points on the test.
3-3. I got 100 points on the test.
(Which one is right?)

Thank you for your help. 3-3 is right, OK? Then what about 3 and 3-1? Are both grammatical?

3-3 is the best.

3 is OK.
3-1 and 3-2 are incorrect.

Thank you, writeacher.

1. How do you get a 100 on a test in math?
(Then this is wrong. Right?)

2. How do you get 100 on a test in math?
(This is right,right? Thank you.)

1 is incorrect; 2 is correct.

When you say sentence 2, it sounds like this:

How do you get one hundred on a test in math?
or
How do you get a hundred on a test in math?

In terms of grammar, all three versions are correct. Let's break them down:

3. "I got 100 on the test." This is a simplified sentence where "100" is used as a noun without the word "points." While it may be grammatically correct, it may sound a little informal or incomplete to some ears.

3-1. "I got a 100 on the test." Here, the word "a" is added before "100" to treat it as a countable noun, with "100" referring to a specific score. This version is arguably more commonly used when referring to a specific number as a score.

3-2. "I got a 100 points on the test." This sentence adds the word "points" after "100" to make it clear that it represents a score. While understandable, this usage is less common in everyday language.

3-3. "I got 100 points on the test." This sentence is also grammatically correct and widely used. It directly states the score without the need for any additional words.

Ultimately, the choice between these versions depends on personal preference, context, and the expected level of formality. If you're writing in an academic or formal setting, it is generally recommended to use the clearer and more standard phrasing, such as "I got 100 points on the test" (3-3).