The number of ways in which 20 different pearls of two colours can be set alternately on a necklace, there being 10 pearls of each colour is :


Correct option is

Twenty pearls ≡ 10 pearls of one color and 10 pearls of another color

Step I : First arrange pearls of same color in 1/2 (10 – 1)!

                             = 1/2 × 9!

Step II : Now arrange pearls of another color in between the arranged 10 pearls in 10! Ways.



The number of divisors a number 38808 can have, excluding 1 and the number itself is :


In a class tournament when the participants were to play one game with another, two class players fell ill, having played 3 games each (not played between them). If the total number of games played is 84, the number of participants at the beginning was:


The number of distinct rational numbers x such that 0 < x < 1 and p/q, where p, q ∈ {1, 2, 3, 4, 5, 6}, is:


Let be the set of 4-digit numbers a1a2a3a4 where a1 > a2 > a3 > a2 then (A) is equal to :


The numbers of number of 9 different nonzero digits such that all the digits in the first four places are less than the digit in the middle and all the digits in the last four places are greater than that in the middle is :


Ten persons, amongst whom are A, B and C are to speak at function. Find number of ways in which it can be done if A wants to speak before B, andB wants to speak before C?


Two teams are to play a series of 5 matches between them. A match ends in a win or loss or draw for a team. A number of people forecast the result of each match and no two people make the same forecast for the series of matches. The smallest group of people in which one person forecasts correctly for all the matches will contain n people, where n is :


Let 1 ≤ m <  ≤ p. The number of subsets of the set A = {1, 2, 3, …,p} having mn, as the least and the greatest elements respectively, is :


The number of 6-digits numbers that can be made with the digits 1, 2, 3 and 4 and having exactly two pairs of digits is :