In how many ways can 4 different books, one each in chemistry, physics, biology and mathematics, be arranged on a shelf?

Four books, one each in Chemistry, Physics, Biology and Mathematics, are to be arranged in a shelf. In how many ways can this be done ?

Four books, one each in Chemistry, Physics, Biology and Mathematics, are to be arranged in a shelf. In how many ways can this be done?

Four books, one each in Chemistry, Physics, Biology and Mathematics are to be arranged in a shelf. In how many ways can this be done?

Four books,one each in Chemistry,Physics, Biology and Mathematics,are to be arranged in a shelf.In how many ways can this be done?

In how many ways 4 mathematics books , 3 physics books, 2 chemistry books and 1 biology book can be arranged on a shelf so that all books of the same subjects are together ?

In how may ways can 15 identical books of mathematics and 12 identical books of physics be placed in a row on a shelf so that tow books of physics may not be together ?

In how may ways can 15 identical books of mathematics and 12 identical books of physics be placed in a row on a shelf so that tow books of physics may not be together ?

In how many ways can 7 different books be arranged on a shelf? In many ways three particular books are always together?