There are 7 red and 5 blue marbles in a jar. In how many ways 8 marbles can be selected from the jar so that at least one red marble and at least one blue marble to remain in the jar?
A. 460
B. 490
C. 493
D. 455
E. 445
OA is D
There are 7 red and 5 blue marbles in a jar. In how many way
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Last edited by rakeshd347 on Mon Sep 30, 2013 5:18 am, edited 1 time in total.
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7R, 5B, --> 8 SELECT
1r3b + 2R2B + 3r1B --> lEFT
=> 7c6 * 5c2 + 7c5 * 5c3 + 7c4 * 5c4
=> 7 * 10 + 21 * 10 + 35 * 5
=> 70 + 210 + 175 = 455
Answer [spoiler]{D}[/spoiler]
1r3b + 2R2B + 3r1B --> lEFT
=> 7c6 * 5c2 + 7c5 * 5c3 + 7c4 * 5c4
=> 7 * 10 + 21 * 10 + 35 * 5
=> 70 + 210 + 175 = 455
Answer [spoiler]{D}[/spoiler]
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To select 8 marbles from 7 red and 5 blue:rakeshd347 wrote:There are 7 red and 5 blue marbles in a jar. In how many ways 8 marbles can be selected from the jar so that at least one red marble and at least one blue marble to remain in the jar?
A. 460
B. 490
C. 493
D. 455
E. 445
OA coming soon.
6R and 2B => 7C6 * 5C2 = 7*10 = 70
5R and 3B => 7C5 * 5C3 = 21*10 = 210
4R and 4B => 7C4 * 5C4 = 35*5 = 175
Total = 70+210+175 = 455
Choose D
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Good ways = Total ways - Bad ways.rakeshd347 wrote:There are 7 red and 5 blue marbles in a jar. In how many ways 8 marbles can be selected from the jar so that at least one red marble and at least one blue marble to remain in the jar?
A. 460
B. 490
C. 493
D. 455
E. 445
Total ways:
Number of ways to select 8 marbles from 12 options = (12C8) = (12*11*10*9*8*7*6*5)/(8*7*6*5*4*3*2*1) = 495.
Bad way 1: No RED marbles left in the jar
For none of the 7 red marbles to be left in the jar, exactly 1 of the 5 blue marbles must be selected.
Number of ways to choose 1 blue marble from 5 options = 5C1 = 5.
Bad way 2: No BLUE marbles left in the jar
For none of the 5 blue marbles to be left in the jar, exactly 3 of the 7 red marbles must be selected.
Number of ways to choose 3 red marbles from 7 options = 7C3 = (7*6*5)/(3*2*1) = 35.
Good ways:
Total ways - bad ways = 495 - 5 - 35 = 455.
The correct answer is D.
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Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
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