Hey all, How about we start preparation for CAT and revision by taking a topic for a day. People with all the Gyan can come in give their valuable posts. People can post questions related to that topic with level based appraoch. People who w…
Hey all,
How about we start preparation for CAT and revision by taking a topic for a day. People with all the Gyan can come in give their valuable posts. People can post questions related to that topic with level based appraoch. People who wanna attempt can attempt by posting there approach so that everyone can understand and if needed a person can find out flaw in their's.
So what's the topic of the day ?
How about we pick up PnC. Many people dread it like me, but i know if u start to get a hang of it, we'll start to enjoy it :)
@Brooklyn said: How about we pick up PnC. Many people dread it like me, but i know if u start to get a hang of it, we'll start to enjoy it
@shadowwarrior : Bhai jaan how about u start explaining the concept of Derragement!! Many ppl dont knw how we get it, n logic behind it, and its use :)
Well I aint good at PnC bt heck, lets start with basics!!
Now:
0!=1 dont forget!!
And = Product
Or= Addition
Eg: From a class of 10 boys and 10 gals teacher wants to chose 1 girl or 1 boy for post of monitor. how many ways??
Ans : One boy can be chosen in 10 ways n a gal 10 ways.
Since its or: Total Ways=10 + 10=20
If question had been:
From a class of 10 boys and 10 gals teacher wants to chose 1 girl and 1 boy for post of monitor. how many ways??
Ans: Total Ways= 10 x 10 = 100
Permutation:
It means ways of arranging objects
Say u have 3 objects, How many ways to arrange it??
Ans : Lets spaces denote places to place obj
_ _ _
Now 1st place can be filled in 3 ways (selecting any 1 object from 3 objects)
Next place with in 2 ways
last place place in 1 way
so total ways= 3*2*1= 6
nPr= Basic Meaning : Arranging r objects out n objects at a time
ie. 4P2 = arranging 2 objects from 4 objects, taking 2 at a time
Eg: A,B,C,D are 4 objects. How many ways can we arrange 2 of them at a time??
Ans: 4P2= 4!/(4-2)! = 4!/2! = 12
The above example can be done with Combination too, but we'll come to that later :)
Some basic q on above topics:
1) Find total ways of arranging letter of the word FOLDER ?
2) Total ways of arranging 4 objects, taking 4 at a time?
3) 5 boys and 5 gals are to be seated in a row. In how many way
a-> All boys together and all gals sit together ?
b-> Boys and Girls sit in alternate Position ?
c-> No 2 gals sit together ( coz guys lyk it dat way 
)
) d-> All gals sit together ( what dey alwz do )
)@Brooklyn said: Some basic q on above topics:1) Find total ways of arranging letter of the word FOLDER ?2) Total ways of arranging 4 objects, taking 4 at a time?3) 5 boys and 5 gals are to be seated in a row. In how many waya-> All boys together and all gals sit together ?b-> Boys and Girls sit in alternate Position ?c-> No 2 gals sit together ( coz guys lyk it dat way )d-> All gals sit together ( what dey alwz do )
1) 6P6=6!
2) 4P4
3) a) 5!x5!
b) BGBGBGBGBG GBGBGBGBGB 5!x2
c) Donno
d) 5!x5!
I know that most of my answers will be wrong, this is my weakest part in QA, please provide the solutions also bhai, so that guys like me can see that and learn. And nice initiative 
@AimIIMAC :
1) 6 different letter we have here.
Now 2 ways to solve this problem:
Method I:
Lets make space filling method-> _ _ _ _ _ _ 6 blanks coz its a 6 letter word
now first place can be filled in 6 ways , next 5 ways and so on till 1
so total= 6*5*4*3*2*1=6!
Method II:
6 objects taking all 6 at a time = 6P6 = 6! :)
2) By same Logic as above : 4P4 or 4!
3)
a-> Lets make all boys 1 group and all gals 1 group. So we have 2 different
these can be arranged in 2P2 or 2! ways
now each group in itself can be arranged in 5P5 or 5! ways
so total ways = 5!* 5! * 2!
b-> Arrangement can be : BGBGBGBGBG
now in this arrangement each boys can be permuted in 5! ways and same for gals
ways= 5! * 5!
or arrangement can be :
GBGBGBGBGB
for this ways = 5! * 5!
Thus Total Ways= 5! * 5! + 5!* 5! = 2*(5! ^ 2)
c-> Lets have 5 boys fixed:
_ B _ B _ B _ B _ B _
Thus in b/w 5 boys we have 6 space. Gals can be seated in any of these
so 6P5 ways arranging gals in it.
Boys can also be permuted so 5! ways
Total Ways = 6! * 5!
d-> All gals together : make them a group
so we have 6 objects to be permuted, ways= 6!
now in d group gals can be permuted in 5! ways
Total ways= 6! * 5!
Hope helps :)
Next set of basic q:
SET 2
1) How many distinct 3 digits no. are there ?
2) How many nos can be formed using digits : 5,4,3,6,9,0. Such that all nos formed are
3) 4 flags of different color are with Mayank. How many signals can he form ?
4) If we form a dictionary with the letter from d word TRIP, at what place would RPIT be ?
Post answers with explanation 😃
Continuing on Dearragement:
Eg I have 5 envelope. Each envelope has 1 correct letter in it. How many ways can i put 2 letter in there correct envelope??
Ans dearrgement (3) * 5c2
@PURITAN : no rather im thinkin NS coz dats more imp and larger topic!! functions later, i wann do all basic and most imp topics first :)