A man buys a certain number of litchies at 20 per rupee and equal number at 30 per rupee. he mixed them and sold them at 25 per rupee. Find his gain or loss percentage.

Researchers conducting web-based research have trouble controlling who actually answers their on-line questionnaires, which places limits on their research due to the possibility of a. biased samples. b. the barnum effect. c. researcher bias. d. research participant bias.