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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 10:45
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to \(\frac{7}{9}\). What is the value of x?


A. 120

B. 160

C. 200

D. 240

E. 360
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D
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 10:57
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Bunuel
A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to \(\frac{7}{9}\). What is the value of x?


A. 120

B. 160

C. 200

D. 240

E. 360
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from given info we can say
40+x * 9 = 7 * ( 120+x)
solve for x ; 240
option D
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 11:32
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Given: A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to \(\frac{7}{9}\).

Asked: What is the value of x?

Probability of selecting a blue marble on a random draw = (40+x)/(120+x) = 7/9
360 + 9x = 840 + 7x
2x = 480
x = 240

IMO D
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 12:14
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As x blue marbles are added, Total marbles= 120+x
blue marbles= 40+x
the probability of selecting a blue marble = (40+x)/(120+x) = 7/9
Therefore, x=240
Option D is correct
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 14:05
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Bunuel
A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to \(\frac{7}{9}\). What is the value of x?


A. 120

B. 160

C. 200

D. 240

E. 360
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Red marbles = 30
Blue marbles = 40
Green marbles = 50

Total marbles = Red + Blue + Green = 30+40+50 = 120

Current probability of selecting a blue marble on a random draw = 40/120

After adding "X" blue marbles, new probability of selecting a blue marble on a random draw will be :
=> (40+X)/(120+X) = 7/9
=> 9(40+X) = 7(120+X)
=> 360+9X = 840+7X
=> 2X = 480
=> X = 240

IMO is D :)
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 15 Oct 2020, 20:48
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to 7979. What is the value of x?


A. 120

B. 160

C. 200

D. 240

E. 360

Explanation: let us assume x blue marbles were added,

then probability of selecting a blue marble on a random draw=40+x/(30+50+40+x)=7/9

40+x/120+x=7/9

360+9x=840+7x

x=240

Hence D is the correct answer
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 16 Oct 2020, 02:25
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Red marbles: 30
Blue marbles: 40
Green marbles: 50

Total marbles: 30 + 40 + 50 = 120

'x' blue marbles are added to the jar and P(B) = \(\frac{7}{9}\)

=> Blue marbles: 40 + x

=> Total marbles: 120 + x

Selecting '1' marble out of (120 + x) marbles : {120 + x}{C_1} = 120 + x

Selecting '1' Blue marble out of (40 + x) marbles : {40 + x}{C_1} = 40 + x

Probability: \(\frac{(40 + x)}{(120 + x)} = \frac{7}{9}\)

=> 9 * (40 + x) = 7 * (120 + x)

=> 360 + 9x = 840 + 7x

=> 2x = 480

=> x = 240

Answer D
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A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and 22 Oct 2020, 10:42
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Bunuel
A jar contains 30 red marbles, 40 blue marbles, 50 green marbles, and no other marbles. After x blue marbles are added to the jar, the probability of selecting a blue marble on a random draw is equal to \(\frac{7}{9}\). What is the value of x?


A. 120

B. 160

C. 200

D. 240

E. 360
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Solution:

After x blue marbles are added, the total number of marbles is 30 + 40 + 50 + x = 120 + x and the total number of blue marbles is 40 + x. Since the probability of randomly selecting a blue marble (after x blue marbles are added) is 7/9, we can create the equation:

(40 + x)/(120 + x) = 7/9

9(40 + x) = 7(120 + x)

360 + 9x = 840 + 7x

2x = 480

x = 240

Answer: D
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