It's not mathematically or grammatically correct - but its meaning is clear enough.
"Save up to 50%!" or "Savings of up to 50%!" would be correct.
Unless they are trying some subtle legal trick of actually reducing the discount from 50% to 25% and claiming that they are telling the truth and that halving the saving is "saving 50% off".
*I got them all correctly. (ungrammatical)
I got them all correct.
I'm assuming here that the Original Poster means that his answers to the question were correct (sentence (1) would be grammatical if the meaning was entirely different). In order to understand why we need to use correct here, and why correctly is wrong, we need to understand the structure of the sentence.
The sentence can be broken down like this:
- Subject: I
- Verb (Predicator): got
- Direct Object: them all
- Predicative Complement: correct
In this type of construction the verb GET takes two complements. The first is a Direct Object, the second is a Predicative Complement.
A Direct Object describes the recipient of some sort of action. It tells us the "patient" in the agent/patient relationship. In this sentence I is the agent, the actor, and them is the patient.
A Predicative Complement, on the other hand, is a complement of the verb that tells us something about the Subject or Object. It describes some attribute. In the following sentence happy is a Predicative Complement that describes the Object, Mary:
- The flowers made Mary happy.
At the end of the process Mary was happy. Notice that we use an adjective there. We cannot use adverbs as Predicative Complements:
- *Mary was happily. (ungrammatical)
- *The flowers made Mary happily. (ungrammatical)
- *Mary seemed happily. (ungrammatical)
We can often use adjectives and nouns as Predicative Complements, sometimes we can even use clauses, but never adverbs. In the type of construction used by the Original Poster, the Predicative Complement describes the Direct Object of the verb. This Predicative complement needs to be an adjective, not an adverb:
- He got them correct.
- He got them wrong.
- *He got them correctly. (ungrammatical - or means something different)
- *He got them wrongly. (ungrammatical - or means something different)
Notice that the last two examples there could be correct if the sentence means something different.These sentences would mean that he obtained or did something in the correct way or in the wrong way - not that the things themselves were correct or wrong.
Best Answer
The second is INCORRECT. (unless that was a typo)
The phrase "turn all of them off" is correct, however.
The stress is different in these two phrases, however. For most uses, the difference between these two is quite subtle, so nothing to worry about.
In the second phrase you can put the emphasis on "THEM"
So, you could say: "Turn all of THEM off" (pointing to a specific set of light switches)
Using the first phrase in like manner sounds awkward.