Official Quant thread for CAT 2013

@chandrakant.k
@Brooklyn
mera logic...3 numbers me se agar 1 number ka bhi unit digit 5 ya 0 hui,,toh it ll be divisible by 5..like 13 x 14 x 15 or 13 x 14 x 20 ...
so 3C2 * 2/10 * 10/10*10/10 = 0.6

@chandrakant.k only 1 number ka ho toh hi chalega na..all 3 jaruri thdi he..they can be
@rkshtsurana said:
@chandrakant.k@Brooklynmera logic...3 numbers me se agar 1 number ka bhi unit digit 5 ya 0 hui,,toh it ll be divisible by 5..like 13 x 14 x 15 or 13 x 14 x 20 ...so 3C2 * 2/10 * 10/10*10/10 = 0.6@chandrakant.k only 1 number ka ho toh hi chalega na..all 3 jaruri thdi he..they can be
flaw in ur logic: u dont know how much digit the number is , ie number can 2 digits, 3 digit so on which would change ur ans
@Brooklyn said:
flaw in ur logic: u dont know how much digit the number is , ie number can 2 digits, 3 digit so on which would change ur ans
dats y i just took unit digit probability na...let it 11111113 x 1111114 x 1111115..
@rkshtsurana said:
dats y i just took unit digit probability na...let it 11111113 x 1111114 x 1111115..
: no your missing the point.

Lets say 3 nos are :ab5, def, kl

u get a value now lets tak no as: x0, d, a ur ans changes
@Brooklyn said:
: no your missing the point. Lets say 3 nos are :ab5, def, kl u get a value now lets tak no as: x0, d, a ur ans changes
bhai ans kese change hga...samaj nhi aa rha

probaility of numbers 0-9 to come at unit digit is equal...we want any one out of 3 numbers to have either 0 or 5 at unit place...so ab5, def, kl and x0 , d, a me as u qouted ,unit digit kch bhi ho na y r we intrsted in it..dimag kharab ho chuka he
@rkshtsurana said:
What would be the probability of product of three positive numbers to be divisible by 5 ?0.20.80.4880.512NOT
@anytomdickandhary sir please see this
@Brooklyn said:
@anytomdickandhary sir please see this
5k 5k+1 5k+2 5k+3 5k+4 be the numbers
probability=1-(4c1+4c2*2+4c3)/(5c1+5c2*2+5c3)=1-(20/35)=3/7?


@rkshtsurana said:
What would be the probability of product of three positive numbers to be divisible by 5 ?0.20.80.4880.512NOT
Consider the total number of numbers to be 5N

Now, each number can be represented as 5k, 5k+ 1, 5k + 2, 5k +3, 5k + 4
So, every form (i.e. 5k + 1 and so on) has N numbers in it

So, probability that the product of three numbers is not divisible by 5 = (4N/5N)^3 = 0.512

So, Probability required = 1 - 0.512 = 0.488 ?
@rkshtsurana said:
What would be the probability of product of three positive numbers to be divisible by 5 ?0.20.80.4880.512NOT
There are 10 possible unit digits, product of the three will not be divisible by 5 is none of the three numbers end in 0 or 5.

So, probability that the product is not divisible by 5 = (8/10)^3

Probability that product is divisible by 5 = 1 - (8/10)^3 = 0.488
Let an = 1111111.....1, where 1 occurs n number
of time. Then,
i. a741 is not a prime.
ii a534 is not a prime.
iii a123 is not a prime.
iv a77 is not a prime.
A. (i) is correct.
B. (i) and (ii) are correct.
C. (ii) and (iii) are correct.
D. All of them are correct.
E. None of them is correct.

Sabko mera ___/\___
@soham2208 said:
Consider the total number of numbers to be 5NNow, each number can be represented as 5k, 5k+ 1, 5k + 2, 5k +3, 5k + 4So, every form (i.e. 5k + 1 and so on) has N numbers in it So, probability that the product of three numbers is not divisible by 5 = (4N/5N)^3 = 0.512So, Probability required = 1 - 0.512 = 0.488 ?
answer seems to be right as shown by @chillfactor sir but

(4n/5n)^3 has repititions,what say?
@rkshtsurana said:
What would be the probability of product of three positive numbers to be divisible by 5 ?0.20.80.4880.512NOT

@Brooklyn

probability that a given number is divisible by 5 = (2/10) = 1/5
so probability that a number is not divisible by 5 = (4/5)
=>probability that none of the three nos. are divisible by 5 = (4/5)^3
=>probability that atleast one of the numbers is divisible by 5 = 1 - (4/5)^3 = 1-0.512 = 0.488.
ATDH.
7 diff object must be divided among 3 people. In how many ways this can be done if at least one of them gets exactly 1 object ???
How many minimum randomly arranged boys do we need to have such that if anyone of them is selected then there is at least 60% chance that he was born in a leap year.?
(a) 3 (b) 4 (c) 5 (d) never possible.
Out of 21 tickets marked with numbers from 1 to 21 , three are drawn at random, find the probability that the three numbers on them are in AP.
@ron123 said:
7 diff object must be divided among 3 people. In how many ways this can be done if at least one of them gets exactly 1 object ???
1218?
@ron123 said:
7 diff object must be divided among 3 people. In how many ways this can be done if at least one of them gets exactly 1 object ???
1 gets 1 object - 3c1*7c1*(6c2+6c3+6c4)
2 get 1 object - 3c2*7c2*2

total = 21*(15+20+15) + 126 = 1176
@19rsb said:
1218?
Right ! 😃 Please share the approach ....
@krum said:
1 gets 1 object - 3c1*7c1*(6c2+6c3+6c4)2 get 1 object - 3c2*7c2*2total = 21*(15+20+15) + 126 = 1176
OA is 1218...
@ron123 said:
7 diff object must be divided among 3 people. In how many ways this can be done if at least one of them gets exactly 1 object ???
The combinations possible are
1) 1 1 5--->7C1*6C1*3!/2!
2) 1 2 4--->7C1*6C2*3!
3) 1 3 3 --->7C1*6C3*3!/2!
4) 1 0 6---->7C1*3!

Add all the terms to get the answer
Please correct me if i am wrong