blitzkriegxX wrote:
There are 15 marbles in a jar consisting of only yellow and white marbles. The probability of choosing 2 white marbles, one after the other, is \(\frac{2}{21}\). How many yellow marbles are in the jar?
(A) 2
(B) 5
(C) 7
(D) 9
(E) 10
Where i went wrong, went too fast to solve this question.
Most important tip -> write in
what you want to calculate
To find -> Yellow marbles Y
Choosing 2 White Marbles, one after the other, will mean
n = number of white marbles
n /15 * (n-1)/14 = 2/21
n^2 - n - 20=0
n^2 - 5n + 4n - 20 =0
( n - 5 ) (n + 4 ) = 0
n =5
Number of Yellow marbles = 15 - n = 15 - 5 = 10
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Quote which i can relate to.
Many of life's failures happen with people who do not realize how close they were to success when they gave up.