Do you say for free or free?
You can use both 'free' and 'for free'. Usually, you use 'free' because 'free' already means without cost or charge. However, 'for free' is a common idiom in English language, and is used as often as 'free'. I can fly to Canada free.
Which is a grammatically correct sentence?
In order for a sentence to be grammatically correct, the subject and verb must both be singular or plural. In other words, the subject and verb must agree with one another in their tense. If the subject is in plural form, the verb should also be in plur al form (and vice versa).