The probability of drawing one red ball from a bag is 2/13.

Question

The probability of drawing one red ball from a bag is 2/13. The bag contains 5 black balls. The number of white balls is 30% less than the number of brown balls and 40% more than the number of black balls. What is the number of red balls in the bag?

(A) 4
(B) 5
(C) 6
(D) 10
(E) 13

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ManifestDreamMBA · Answer

Black = 5
White = 1.4 *5 = 7
Brown = 7/0.7 = 10
Red be R
Total = 5+7+10+R = 22+R

R/22+R = 2/13
13R = 44 + 2R
11R = 44
R = 4

Dereno · Answer

Probability of selecting one red ball = 2/13

5 black balls = B

White balls W = (7/10) Brown balls Br . Thus  W : Br = 7:10

White balls W = (1+2/5) B . W = (7/5)* B . Thus,  W: B = 7:5

Since, black balls = 5.  We don’t need to alter the ratio.

Let R denote the number of red balls.

Total balls = 7:10:5:R = 22+R

We are selecting one Red ball from R red balls = R C 1

RC1/ 22+R = 2/13

so denominator should be a multiple of 13. 22+R = 13K = 26 .

Then  the number of red balls = 4 . ( R = 26-22=4)  OPTION A

Ayeka · Answer

P(R)=2/13 = R/(R+A+W+B) 
(Number of black balls) B=5 
(Number of white balls) W= 0.70 of A (Number of brown balls) 
W:A= 7:10
Also, W= 1.4 B ; W =(7/5) B ; W= 7 and A= 10 
Total number of balls= R+A+W+B = R+10+7+5= R+22

R/(22+R)= 2/13 
13R=44+2R
11R=44 
R=4

Answer: A

rohitz98 · Answer

Given the red ball's probability is 2/13
number of black balls is 5
no of white balls is 20% more than black balls. Hence its 7
its 30% less than no. of brown balls. Which gives no. of brown balls is 10

To total of black, brown and white balls is 22.
If 4 red balls are added then the total becomes 26 and the probability of red ball is 2/13
Hence  Option A

helloThere96 · Answer

P(Drawing a red ball from a bag) = 2/13 = 2x/13x

# of red balls = 2x
Total # of balls = 13x

# of black balls = 5
# of white balls = 1.4 * # of black balls = 1.4 * 5= 7
# of white balls = 0.7 * # of brown balls = 7
# of brown balls = 7/0.7 = 10

Number of non-red balls = 13x - 2x = 11x = # of black balls + # of white balls + # of brown balls 
11x = 5 + 7 + 10
11x = 22
x = 2

# of red balls = 2x = 2 * 2 = 4

Option A is the answer

bhargavhhhhhhhh · Answer

Let:
- r = number of red balls
- b = 5 (black balls)
- w = number of white balls
- n = number of brown balls

Step 1: w = 0.7n (white balls 30% less than brown)
Step 2: w = 1.4b = 7 (white balls 40% more than black balls)
Step 3: 7 = 0.7n, n = 10 (brown balls)
Step 4: Total balls = r + 5 + 7 + 10 = r + 22
Step 5: Probability = r / (r + 22) = 2 / 13
Step 6: 13r = 2(r + 22), solve for r:
 13r = 2r + 44
 11r = 44
 r = 4

Answer: 4 red balls.

Abhiswarup · Answer

P(one Red Ball)=2/13
Black Ball=5
White Ball = 1.4*5=7
Brown Ball=X
White Ball= 0.7X=7, X=10
Total Balls= 10+7+5+R
P(one red ball)=RC1/(22+R)=R/22+R=2/13
R=4
Answer is A.

The probability of drawing one red ball from a bag is 2/13.

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The probability of drawing one red ball from a bag is 2/13.

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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Perfect 805 Score Debrief by Julia

My Rewards