We have no less than a thousand students in our College.
The teacher was very angry at his student.
be angry with someone : to feel or express displeasure
be angry at something : to be irritated by
Here, angry with is the right usage.
I bought four dozen mangoes.
dozen is always used in the Singular form after numerals.
After the letter reached me, I shall know the result.
Simple Present Tense-reaches will be used.
The clause has started with after . In such cases, Simple Present Tense is used.
Hence, After the letter reaches is the right usage.
The transport workers have organised a strike asking for more salary.
Here, demanding is the right usage.