GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 20 Nov 2019, 16:01

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

A box contains 20 balls: 10 white and 10 black. The balls can be drawn

Author Message
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 59182
A box contains 20 balls: 10 white and 10 black. The balls can be drawn  [#permalink]

Show Tags

02 Oct 2018, 02:28
1
1
00:00

Difficulty:

15% (low)

Question Stats:

85% (01:54) correct 15% (02:35) wrong based on 53 sessions

HideShow timer Statistics

A box contains 20 balls: 10 white and 10 black. The balls can be drawn at random. If the first three drawn balls are black, what is the probability that the next two drawn balls will also be black?

(A) 21/136
(B) 4/17
(C) 1/3
(D) 4/7
(E) 2/5

_________________
Director
Joined: 20 Feb 2015
Posts: 737
Concentration: Strategy, General Management
Re: A box contains 20 balls: 10 white and 10 black. The balls can be drawn  [#permalink]

Show Tags

02 Oct 2018, 06:47
Bunuel wrote:
A box contains 20 balls: 10 white and 10 black. The balls can be drawn at random. If the first three drawn balls are black, what is the probability that the next two drawn balls will also be black?

(A) 21/136
(B) 4/17
(C) 1/3
(D) 4/7
(E) 2/5

3 black balls are already drawn , remaining are 7 black and 10 white balls
number of ways we can draw two black balls from remaining = $$7c2$$
total number of ways we can draw two balls = $$17c2$$
required probability = $$7c2$$ / $$17c2$$ = 21/136
Re: A box contains 20 balls: 10 white and 10 black. The balls can be drawn   [#permalink] 02 Oct 2018, 06:47
Display posts from previous: Sort by