In eng. entrance exams which class more matters for qualifying exam eg. viteee, jee,comedk,etc.
See, every entrance exam of Engineering has a different patterns, different question, different difficulties levels in the question etc and also lot depends on the candidates that are appearing for exams.Both class 11 as well as 12 is important fir a strong base.There is no specified syllabus or weightage.So, you should focus in these thing as thing can hamper your performance. Though getting a rough idea about important chapters and know about chapters that carry kore weightage is definitely a good idea but deep keep in mind that pattern of every exam is different so you must go through them.
I hope this helps.
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