I am struggling with choosing the suitable pronoun in the following sentence.
He wrote other / another two letters in just 15 minutes.
My intuition tells me that in this case, ‘another’ is the pronoun that should be used–as it makes the most sense as far as the context (he has written the letters in just 15 minutes) is concerned. But, on the other hand, a friend of mine claims that either the use of ‘other’ here is correct or it is the only option by using which the sentence is grammatically correct.
The question is: are both of these pronouns grammatically and logically correct, or is there an only option? If so, which one is it? Thank you in advance.