Permutations & Combinations - Questions & Discussions

mbafrmfms Says
Anyone?????????????????

I solved it this way but am mot 100% sure..
MATHEMATICS has 2M , 2 A , 2T and 5 other letters.Three cases arise:
case1- when all letters are distinct. E has to be there and remaining four letters can be selected in 7C4 ways. So, 7C4*5! =1050
Case2- when 2 pair of letters are alike (ie AAETT)
(3C2*5!)/2!*2! =90 (3C2 for selecting 2 letters from M,A,T)
case3-when 1 pair of letter is alike (ie AAEIS or ETTIC)
(3C1*6C2*5!)/2!=2700
But I am getting total 3840 ways only

Hello Puys, Kindly have a look at the problem below:

Question
A cricket team of 11 players is to be selected from 18 players, of whom 10 are batsmen, 6 are bowlers and 2 are wicketkeepers. If the team should have at least 4 boowlers and atleast 1 wicketkeeper, the number of ways in which the team can be formed is?

A) 15000
B) 14550
C) 17850
D) 14904
E) 15800


Now, the thing is that I know the answer to this question which is determind by making different situations on the number of bowlers, batsmen & WC as follows and then making combinations:
BAT BOWL WC
6 ..... 4 .... 1
5 ..... 5 .... 1
4 ..... 6 .... 1
5 ..... 4 .... 2
4 ..... 5 .... 2
3 ..... 6 .... 2

Now please look here, why cant we solve this problem as follows:
(Selecting 4 bowlers out of 6) x (Selecting 1 WC out of 2) X (Selecting 6 players out of remaining 13 players)
Please tell me the problem with the above logic, I know it's wrong but can not figure out as to why it is wrong.

Please help. Thank you.

Hello Puys, Kindly have a look at the problem below:

Question
A cricket team of 11 players is to be selected from 18 players, of whom 10 are batsmen, 6 are bowlers and 2 are wicketkeepers. If the team should have at least 4 boowlers and atleast 1 wicketkeeper, the number of ways in which the team can be formed is?

A) 15000
B) 14550
C) 17850
D) 14904
E) 15800


Now, the thing is that I know the answer to this question which is determind by making different situations on the number of bowlers, batsmen & WC as follows and then making combinations:
BAT BOWL WC
6 ..... 4 .... 1
5 ..... 5 .... 1
4 ..... 6 .... 1
5 ..... 4 .... 2
4 ..... 5 .... 2
3 ..... 6 .... 2

Now please look here, why cant we solve this problem as follows:
(Selecting 4 bowlers out of 6) x (Selecting 1 WC out of 2) X (Selecting 6 players out of remaining 13 players)
Please tell me the problem with the above logic, I know it's wrong but can not figure out as to why it is wrong.

Please help. Thank you.




cases are:

W Bow Bat

1 4 6=2C1*6C4*10C6=6300
1 5 5=2C1*6C5*10C5=3024
1 6 4=2C1*6C6*10C4=420
2 4 5=2C2*6C4*10C5=3780
2 5 4=2C2*6C5*10C4=1260
2 6 3=2C2*6C6*10C3=120

total = 14904

How many 5 digit numbers exist having exactly two 4s in them?


_ _ _ 4 4=8*9*9=648
_ _ 4 _ 4=8*9*9=648
_ 4 _ _ 4=648
_ 4 4 _ _=648
_ 4 _ 4 _=648
_ _ 4 4 _=648

now rest combinations will have 4 on 1st place so,we need not to worry about 0 on 1st place

9*9*9=729*4=2196

total cases would be 648*6+2196=6804
cases are:

W Bow Bat

1 4 6=2C1*6C4*10C6=6300
1 5 5=2C1*6C5*10C5=3024
1 6 4=2C1*6C6*10C4=420
2 4 5=2C2*6C4*10C5=3780
2 5 4=2C2*6C5*10C4=1260
2 6 3=2C2*6C6*10C3=120

total = 14904


Atleast read what I'm asking, I know the answer is 14904, I'm asking why the second logic is flawed. Thnx.
Question
A cricket team of 11 players is to be selected from 18 players, of whom 10 are batsmen, 6 are bowlers and 2 are wicketkeepers. If the team should have at least 4 boowlers and atleast 1 wicketkeeper, the number of ways in which the team can be formed is?

Now please look here, why cant we solve this problem as follows:
(Selecting 4 bowlers out of 6) x (Selecting 1 WC out of 2) X (Selecting 6 players out of remaining 13 players)


We can not do it like this, as there is lot of overcounting. Consider following ywo cases:-

i) You choose b1, b2, b3, b4, then w1 and then choose b5, B1, B2, B3, B4, B5
ii) You choose b2, b3, b4, b5, then w1 and then choose b1, B1, B2, B3, B4, B5

Both the cases are different but you counting them same. Similarly there are many repetitions
We can not do it like this, as there is lot of overcounting. Consider following ywo cases:-

i) You choose b1, b2, b3, b4, then w1 and then choose b5, B1, B2, B3, B4, B5
ii) You choose b2, b3, b4, b5, then w1 and then choose b1, B1, B2, B3, B4, B5

Both the cases are different but you counting them same. Similarly there are many repetitions


Oh Yes, You're right.. Hmm.. Silly me.. :shocked:
Thank You

Sorry for this silly que bt m nt getting the answer given in the book ...
The no. of ways that 7 person can address a meeting so that three persons A,B and C from them A will speak before B and B before C is?
840 or 720?

Sorry for this silly que bt m nt getting the answer given in the book ...
The no. of ways that 7 person can address a meeting so that three persons A,B and C from them A will speak before B and B before C is?
840 or 720?


My take is 840.

Maximum arrangements = 7!.
But from A, B and C; out of 3! arranagements only 1 is what we need.
So, out of 7!; we will need 7!/3! = 840.

ur ans is right but pls explain it in simple terms bhai...just nw i started this topic
ABC _ _ _ _
so m doing 5! * but then how to proceed next

Sorry for this silly que bt m nt getting the answer given in the book ...
The no. of ways that 7 person can address a meeting so that three persons A,B and C from them A will speak before B and B before C is?
840 or 720?


x.....A.....y.....B.....z.....C.....s

x+y+z+s = 7-3 = 4

Solutions : C(7,3) : 35.

But the remaining can also be permuted in 4! = 24 ways

So my take is 35*24 = 840.
ur ans is right but pls explain it in simple terms bhai...just nw i started this topic
ABC _ _ _ _
so m doing 5! * but then how to proceed next


What wrong you are doing here is that nowhere its given that ABC should be together there can also be speakers b/w A,B,C.

Its just given A should speak before B before C and in b/w other speakers may also be there.

Hope you got your mistake.:D

Question :

In how many ways 10 identical presents be distributed among 6 children such that none gets zero.


Ans : I am using the logic
0000000000 Let these be the 10 objects ,Now to divide them i need to put 5 sticks b/w them.
000\000\000\000

this can be done in 9c5 ways . but the answer is 15 c5 . kindly help , where am i going wrong

Question :

In how many ways 10 identical presents be distributed among 6 children such that none gets zero.



Each one gets atleast 1.
So, 6 are given. Remaining 4 can be given like this:
a+b+c+d+e+f = 4 => 9C5 ways to this.

If 0 presents are allowed, then answer will be 15C5. So, looks like a mistake in OA.
a+b+c+d+e+f = 10 => 15C5

how many 4 digit numbers that are divisible by 3,can be formed using the digits 0,1,2,3 and 8 if no digit is to occur more than once in each number?

rajr Says
how many 4 digit numbers that are divisible by 3,can be formed using the digits 0,1,2,3 and 8 if no digit is to occur more than once in each number?


My take is 36.

0+1+2+3+8 = 14
14%3 = 2
So, we need to remove either 2 or 8 to make sum of digits divisible by 3.

Case 1: 0, 1, 2, 3 => _ _ _ _ => 3*3*2*1 = 18 numbers
Case 2: 0, 1, 3, 8 => _ _ _ _ => 3*3*2*1 = 18 numbers

Total 36.
rajr Says
how many 4 digit numbers that are divisible by 3,can be formed using the digits 0,1,2,3 and 8 if no digit is to occur more than once in each number?


bad :banghead:

The probability of a missile hitting a target is 1/2 and it takes 3 missiles to destroy a bridge, atleast how many missiles should be fired such that the probability of destroying the bridge is greater than 0.999

Ans is 7.

Can anyone please sove this clearly and help me.?

6 people have to go to attend a meeting in 3 different vehicles, each of which can accommodate 6 persons. In how many ways they can go so that they use all the three vehicles?

Please solve this with clear steps.

there is no constraints like, the boxes have not to b filled up by more than one balls?