For calculating LD50 by any one method, find out the least tolerated (smallest) dose (100% mortality) and most tolerated (highest) dose (0% mortality) by hit and trial method. Once these two doses are determined, select at least 5 doses in between the least tolerated and most tolerated doses, and observe mortality due to these doses. Then apply correction factor to 0% and 100% mortality group[for 0% dead = 100(0.25/n) and for 100% dead = 100x(n-0.25/n), where n = number of death]. The percentage mortality values are converted to probit values by reading the corresponding probit units from the probit table.
Plot the probit value against log doses and read LD50 value as the dose that corresponds to probit 5.