Probability - 10 marbles

if we assume gals select white marble then answer is:-
(5/10)*(4/9)*(3/8)*(2/7)*(1/6)=1/252
also they all can choose black marble so answer is:-
again 1/252
combining both
1/126 option (A)

Any problem with my logic?????

Please help me with this problem

If Jim earns x dollars per hour, it will take him 4 hours to earn exactly enough money to purchase a particular jacket. If Tom earns y dollars per hour, it will take him exactly 5 hours to earn enough money to purchase the same jacket. How much does the jacket cost?
(1) Tom makes 20% less per hour than Jim does. (2) x + y = $43.75

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puneetgrover wrote:Please help me with this problem

If Jim earns x dollars per hour, it will take him 4 hours to earn exactly enough money to purchase a particular jacket. If Tom earns y dollars per hour, it will take him exactly 5 hours to earn enough money to purchase the same jacket. How much does the jacket cost?
(1) Tom makes 20% less per hour than Jim does. (2) x + y = $43.75

The amount Jim must earn to buy the jacket = (number of hours)(hourly rate) = 4x.
The amount Tom must earn to buy the jacket = (number of hours)(hourly rate) = 5y.
Since the amount is THE SAME in each case, we get:
4x = 5y.

Statement 1:
If x=10 and y=8, then the cost of the jacket = 4x = 4*10 = 40.
If x=100 and y=80, then the cost of the jacket = 4x = 4*100 = 400.
Since the cost of the jacket can be different values, INSUFFICIENT.

Statement 2:
Since we have two variables (x and y) and two distinct linear equations (4x=5y and x+y = 43.75), we can solve for x and y.
Thus, the cost of the jacket can be determined.
SUFFICIENT.

The correct answer is B.

puneetgrover wrote:Please help me with this problem

If Jim earns x dollars per hour, it will take him 4 hours to earn exactly enough money to purchase a particular jacket. If Tom earns y dollars per hour, it will take him exactly 5 hours to earn enough money to purchase the same jacket. How much does the jacket cost?
(1) Tom makes 20% less per hour than Jim does. (2) x + y = $43.75

From the prompt, 4x = 5y.

S1:: y = (4/5)x. Same as the original equation, not sufficient.
S2:: x + y = 43.75. Combining this with 4x = 5y gives two independent linear equations, two variables, so sufficient. To solve, just replace x with (5/4)y, then do (5/4)y + y = 43.75.

Hi all,

I have approached it this way, can someone confirm if my method is right

5 girls can choose same colored marbles in the following way

5*4*3*2*1(i,e 1st girl has 5 ways of choosing the first marble, 2nd girl has 4 ways of choosing the same colored marble and so on)

now the total no of ways the girls can choose the marble is - 10*9*8*7*6

now - desired outcome/total outcome = (5*4*3*2*1)/(10*9*8*7*6) = 1/252
last step(the girls can choose from either of the colors) so 2*(1/252) = 1/126 (ans A)

Brent@GMATPrepNow wrote:The answer is, indeed, A (1/126)
Here's my solution:
The easiest/fastest way to determine the probability is to examine the probability of each necessary outcome to guarantee that the girls (and subsequently the boys) draw the same colored marble.
We get [P(1st girl selects any marble) x P(2nd girl selects marble the same color as 1st girl) x P(3nd girl selects marble the same color as 1st girl) x P(4th girl selects marble the same color as 1st girl) x P(5th girl selects marble the same color as 1st girl) x P(boys getting same color ball from remaining balls)
This equals: 1 x 4/9 x 3/8 x 2/7 x 1/6 x 1
Which equals: 1/126

Why does P(boys getting same color ball from remaining balls = 1?

Never mind. I figured it out!

I hope it will be useful to show the following logic and how I have got 1/126
Maybe for some of you, it will be easy to remember ( I hope, it works for me at least)

P=m/n

m=2*C (5:5)= 2*5!/5!0!=2

Where
Clasic formula
C(n:r) = n!/r!(n-r)!
Short version
C(n:r) = first r values of n!/ r!

n=C(5:10)=10!/5!5!=10*9*8*7*6/5*4*3*2*1=252

P=2/252=1/126 $$$$