Purple underpants with a red checkmark become best sellers online prior to the national college entrance examinations. Photo: Screenshot of Btime video

Purple underpants became all the rage prior to China's national college entrance exams as they were said to bring good luck. 

An e-commerce seller on Taobao surnamed Wang, told the Btime that since May he had sold several hundred purple underpants that also had red checkmark. 

In Chinese the color purple is pronounced zi, while butt is pronounced ding. People wearing such underwear will have a purple butt, or zi ding, which sounds similar to the phrase "100 percent sure." Therefore, some students leave nothing to chance in the hope of getting 100 percent on their exams.

Some mothers also wore red qipao, hoping to give a good start to their children.

The annual college entrance exams starting on June 7, also known as gaokao, determine the future academic careers of some 10 million students each year, so parents and students often seek auspicious objects to help. 

If you don't like purple, an alternative might be wearing Nike, a Net user said jokingly on Twitter-like Sina Weibo. 

Netizens also shared other auspicious customs for the exams, such as preparing offerings to Confucius statues as the ancient sage was believed to bring good luck for test takers. 

Weibo user "Jiaoyao" said she didn't wash her hair before the exams because it could wash away the knowledge. 

Global Times