There are three identical red balls and fouridentical blue balls in a bag. Three balls are down. The number of different colour combination is
A.  20 
B.  35 
C.  40 
D.  30 
Option: D Explanation : 
How many five different letter words can be formed out ofthe word "LOGARITHMS"?
A.  20120 
B.  30120 
C.  30240 
D.  40840 
Option: C Explanation :
Total letters in the word "LOGARITHMS" is 10,i.e. n=10 and we have to form fiveletter words
= 10 x 9 x 8 x 7 x 6 = 30240 
Given np_{r} = 3024
Value of r will be
A.  3 
B.  4 
C.  6 
D.  9 
Option: B Explanation : Since ^{n}p_{r} is product of consecutive positive integers. ^{n}p_{r} = 3024 = 9 x 8 x 7 x 6 Hence, r = 4 
A.  20 
B.  30 
C.  60 
D.  120 
Option: C Explanation : First three jobs can be filled by 5 members in ^{5}P_{3} ways. Number of ways of filling the first 3 jobs
^{5}P_{3 }= 5 x 4 x 3 = 60 ways
