I see my friend doing exam. He never look for answers when he doing his exam (rarely cheat on exam) and until the 3rd exam he looks for the answers on his notebook during his exam then he started to do it frequently (not every time when he doing an exam) What should I say? Should I say "Jamie started to cheat on exam frequent?" Or "Jamie cheat on exam quite frequent" those sentence looks weird for me. Any ideas?
The idiom on the increase may meet your English need. TFD
increasing, or growing steadily or rapidly.
"Jamie's cheating on exams was on the increase"
One thing to notice is that "frequent" in your sentence is modifying "cheat" which is a verb, so you should use an adverb (frequently) instead instead of an adjective (frequent).
Jamie cheated on his exams quite frequently.
If you wanted to use "frequent" you would need need to change "cheat" to "cheating".
Jamie's cheating was quite frequent.
That just means that it happened often. If you want to say the number of times that Jamie cheated was increasing, you would use "more frequent(ly)":
- Jamie was cheating on his exams more frequently.
- Jamie has started to cheat on his exams more frequently.
- Jamie's cheating has become more frequent.