As far as I know the weightage of your class 12 marks in physics chemistry maths is 50% rest 50 will depend upon your KCET marks in physics chemistry maths and with the combination of both you KCET rank will be calculated. Its eligibility criteria says that the candidates should have scored at least 45 percent aggregate marks in the three subjects in the qualifying examination. So you need to keep that in mind.

For any furthur information about the eligibility criteria of KCET you can visit the webisite given below.

https://engineering.careers360.com/articles/kcet-eligibility-criteria

Good Luck!!