another way to do it alltho lengthy is work at the job for 2 hours.
it takes a while longer but i think it quadruples you're chance to get the item (20%for 30 minutes 80% for 2 hours) not sure if it works or not but when i've done jobs for 2 hours very often have a i got the product and sometimes even a stylish hat
but the time scales are very delicate sometime 3 10 minute jobs can get you a little more than a half hour job 4 half hours may or not not yield as much as 2 hours same with hours i'd be quite interested to know which turned out to be the best use of time/yield