Question

a person bought 100 articles for rs. 4000. he sold 20 of them at gain of 5%. at what percent of profit will sold the remaining articles so that he would gain 20% of profit in whole.

Answer 1

20% profit on the whole would be equal to 4000*120/100= 4800
20 articles were sold at 5%profit.
20 articles=800rs.
5%profit=800*105/100=rs 840
now, to make 20% profit on the whole, he needs to sell the other 80 articles at rs 4800-840=  3960rs. 
price of 80 articles = 3200 rs. now, the profit % he should sell at in order to have 20% profit on the whole= 3960-3200/3200*100
= 760/3200*100
=76/320*100
= 23.75%