Exams › IBPS PO › Quantitative Aptitude

Box: 6 blue, y white, (y+4) black balls. P(white)=1/4. If 2 balls drawn simultaneously, find P(both black).

1. 18/95
2. 55/43
3. 21/19
4. 33/25

Correct answer: 18/95

Solution

P(white)=y/(6+y+y+4)=y/(2y+10)=1/4. 4y=2y+10 → y=5. White=5, Black=9, Total=20. P(2 black)=C(9,2)/C(20,2)=36/190=18/95.

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