If the best and the worst paper never appear together, find in how many ways six examination papers can be arranged.

A question paper contains 20 questions in how many ways can 4 questions be attempted?

A boy appears for 5 papers , each of the same number of maximum marks .He scores in each of the papers in the ratio of 6 : 7:8:9:10 .If his average score in all the five papers together was 60% , then in how many papers did he get more than 50% marks ?

A question paper contain 15 questions. In how many ways can 7 questions be attempted?

In how many ways can 12 papers be arranged if the best and the worst paper never come together?

In an examination, there are 8 candidates out of which 3 candidates have to appear in mathematics and the rest in different subject. In how many ways can they be seated in a row, if candidtes appearing in mathematics are not to sit together ?

Six students are contesting the election for the presidentship of the students' union. In how many ways can their names be listed on the ballot papers?