In how many ways can 5 girls be seated in a row so that two girls Ridhi and Sanya are:
(a) always together (b) never together
Number of digit available = 5 (all distinct)
Number of digits to be used = 5
Since the number is not divisible by 5.
5 cannot occupy box 5.
Number of permutations for box ...(i)
Now, we have 4-digits and 4 boxes.
Number of permutations = ... (ii)
From (i) and (ii), the total number of permutations = 4 x 24 = 96
Hence, the number of numbers formed, that are not divisible by 5 = 96.
(b) there is no restriction as to the number of prizes that a boy may get.
(c) no boy sets all prizes.
There are 8 students appearing for an examination, of which 3 appear in mathematics paper, and 5 in other different subjects. In how many ways can they be seated if
(a) all the students appearing for mathematics paper are together.
(b) the students appearing for mathematics paper are not all together.
(c) no two students appearing in mathematics paper are seated together ?