Your son's rank can be predicted by using the formula, (100-your total percentile)*869010/100. In your case, your approximate rank would be 30328. Now if your son belongs to Karnataka, he has the advantage at NIT Surathkal. But going by previous year cut offs mentioned in our page: https://engineering.careers360.com/articles/jee-main-cutoff-for-nit-surathkal, it might be tad difficult. But cut offs change evrey year depending on various factors. Please check the cut offs of previous years of NITs at our page: https://engineering.careers360.com/articles/jee-main-cutoff . You can also predict colleges using our college predictor: https://engineering.careers360.com/jee-main-college-predictor?