A diet is a fasting period of one type or another. Your interpretation seems to be something other than the actual meaning:
Meanwhile, there was a particular diet that I failed the Quantitative Technique paper and I was the one who taught those who passed the paper.
A tip :
Use a grammar checker and a tool like Google Docs to write your stories.
The examination usually takes place twice a year. The months of April and October. Each month, we used to call it the April diet and the October diet.
Thank you for your comments and support. And advice is noted for better results.