PLEASE SOLVE.....

[mermaid1787]

Hey I've across these questions and was unable to solve them!

1.Given there are 3 sets R1=(1,2,3) R2 =(-1,-2,-3) and R3=(-3,-2,-1,1,2,3) and their standard deviations are S1 ,S2, S3 respectively. so,
1)S1>S2
2)S2<0
3)S3=0

2.There are 10 balls and 10 bags and 3 balls are of same kind.In how many ways these 10 balls can be arranged in these 10 bags so that no bag is left empty?

3. What is the remainder of the expression (7^0,7^1,7^2........7^20) when divided by 14?

4. The reflection of the positive digit number is obtained by reversing the digits.FOR example ,321 is the reflection of 123. The difference between a five digit number and its reflection MUST be divisible by which of the foll?
A.2
B.3
C.5
D.6
E.9

[traum]

4. The reflection of the positive digit number is obtained by reversing the digits.FOR example ,321 is the reflection of 123. The difference between a five digit number and its reflection MUST be divisible by which of the foll?
A.2
B.3
C.5
D.6
E.9


B. 3

the best strategy here is elimination if something is divisible by 6 and 9 then it must be divisible by 2 and 3, so they are eliminated. 5 is easily eliminated by a simple trial which leaves 2 and 3... you can only get 2 if the last digit and the first digit are both odd or even, which is clearly not true for all numbers (e.g. 58642 - 24685) so a good guess is 3... is this right?


2.There are 10 balls and 10 bags and 3 balls are of same kind.In how many ways these 10 balls can be arranged in these 10 bags so that no bag is left empty?

hmm not sure about this question - surely 10C10 = 1 way? i.e. 1 ball per bag? any other way will leave at least 1 bag empty

Unless they meant 10 different balls AND another 3 balls - i.e. 13 balls and 10 bags, in which case the answer is 858.

3. What is the remainder of the expression (7^0,7^1,7^2........7^20) when divided by 14?

what do you mean by the comma? is it a * sign? i.e. 7^0*7^1 etc... in which case the answer should be 7

[Abaabeel]

Q4. I think the better way to solve this question is that lets assume the 3 digit number as abc where a is 100th, b is 10th and c is unit digit. Their reflection would be c as 100th, b as 10th and a as unit digits. now lets set up the equation as (100a+10b+c)-(100c+10b+a)= 99a-99c= 99(a-c)...so it is divisible by 9. The same if extended to 5 digit number it will be divisible by 9.

[totymody]

Q1- there is no correct anwer :
I tried it by calculation :

mean 1 = 6/3 =2
S1= sqrt (2/3)

mean2 = -6/3 = -2
S2=sqrt(2/3)

mean3=0
S3=Sqrt(28/6)

, so no choice is correct.


Q2-
I am quit sure from the answer, but i am not sure if my explanation is right. i tried to solve it by more simple example if we have 5 balls and 5 bags and 3 of them are the same.

we have 10 balls to be arranged in 10 bags , but 3 balls (of the ten) are the same . so the problem turns to be like if we have 7 bags and want to arrange 10 balls in them with out repetition and the order is important.

so 10p7 = 10!/(10-7)!=10*9*8*7*6*5*4

Q3-the remainder is 1

Q4- try any 5 digits number : ex. 54321, the reflex is 12345.

subtract 12345 from 54321 = 54321-12345=41976

sum the 5 digits : 4+1+9+7+6 = 27, hence 27 divisible by 9, so the answer is e.9

[walt526]

Originally Posted by mermaid1787

Hey I've across these questions and was unable to solve them!

1.Given there are 3 sets R1=(1,2,3) R2 =(-1,-2,-3) and R3=(-3,-2,-1,1,2,3) and their standard deviations are S1 ,S2, S3 respectively. so,
1)S1>S2
2)S2<0
3)S3=0

FYI, this question was on my GRE that I took on Tuesday, 10/27/09.

The correct answer is NONE.

S1=S2
S2>0 since S2=sqrt[var(R2)]
S3>0 since var(R3) is not zero (i.e., each element of R3 is not equal to the mean, 0)