Question

in how many ways can 21 books an English and 19 books on Hindi...be placed in a row on a shelf so that 2 books on Hindi may not be together?​

Answer 1

there are 20 places between 21 english book and 2 places (first and last)

totally 22 places for 19 hindi books

so we select 19places from 22 places for hindi books

so number of ways =22C19

=22C3=22(21)(20)/1(2)(3)

=11(7)(20)=1540