46. There is a circular table and 60 people can sit in that. If there are N number of people sitting and amonster comes and want to occupy a seat such that he has someone on his side. What is the minimum value of N?
a) 15
b) 20
c) 29
d) 30
Say, one person is sitting in seat no. 2 then d monster sits in seat no. 1 or 3 (monster will find a person beside it)
Again there is a person sitting in seat no. 5, then d monster can sit in seat no 4 and 6...
again there is a person sitting in seat no. 8
Thus d pattern of ppl sitting is-
sit no. 2,5,8,11,14,17,20,23,26,29,32,35,38,41,44,47,50,53,56,59
thus min no. of n is 20
47. How many 3 digits numbers less than 1000 are there in which, if there is a 3 it is followed by 7? Given that no two digit of the number should be same.
suppose d 3 digit no. starts with 1
10__(This blank space can b filled in 7 ways 2,4,5,6,7,8,9)
in d above case we cannot take 3 since it should be followed by 7 which is not possible here.
now we take-
11__ this space can also be filled in 7 ways
12__ 7 ways
13__ this space can be filled only by 1 way and dat is 7.
14__ again 7 ways
15__ 7 ways
16__ 7 ways
17__ 7 ways
18__ 7 ways
19__ 7 ways
that gives us 57 ways in total
We will follow d same procedure for 3 digits starting with 2,4,5,6,8,9(but not in case of 3 and 7)
thus we get 57*7= 399 ways
now lets check condition for 3. 3 is always followed by 7 and nothing else
thus
37__ this space can be filled in 8 ways(0,1,2,4,5,6,8,9)
no other condition is possible in case of 3.
that makes our total to be 399+8=407
now lets check condition for 7
70__ this can be filled in 7 ways
71__ 7 ways
72__ 7 ways
73__ this condition is not possible since 3 should be followed by 7 but we cannot repeat 7.
74__ 7 ways
75__ 7 ways
76__ 7 ways
78__ 7 ways
79__ 7 ways
this gives us 56 ways
therefore our total becomes 407+56=463 and this is the answer.
48. How many numbers are there between 1100 - 1300 which are divisible by and that all 4-digits of number should be odd (ex:1331)