If N is related to Datsun, H is related to Mahindra,

Solution

J and the one who uses Volvo attend the seminar on a month which has less than 31 days. Three persons attend the seminar between J and the one who uses Volvo. J does not attend the seminar on even number date. The one who uses Bentley attends the seminar in 7th of October E attends the seminar immediately after N. Three persons attend the seminar between E and the one who uses Mercedes. J does not use Mercedes. The one who uses Mercedes attends the seminar after E. N attends the seminar on even number date. Two persons attend the seminar between H and the one who uses Mercedes. H does not use Volvo. Neither N nor E uses Volvo. Numbers of persons attend the seminar before K is two less than the numbers of persons attend the seminar after the one who uses Ferrari. K attends the seminar before the one who uses Ferrari. D attends the seminar immediately after the one who uses Ferrari. Case 2(a) and 2(o) will be dropped because Number of persons attends the seminar before K is two less than the number of persons attend the seminar after the one who uses Ferrari. Number of person attends the seminar before the one who uses Toyota is same as the number of person attends the seminar after the one who uses Datsun. H and K neither uses Toyota nor uses Datsun. N does not use Datsun. Number of person attends the seminar before A is same as the number of person attends the seminar after C. The one who use Honda attends the seminar immediately after C. Only one person attends the seminar between Z and the one who uses Mahindra. Three persons attend the seminar between U and the one who use audi. Case 3 will be dropped because the one who uses Audi attends the seminar before the one who uses Mahindra, but not immediate before.