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# A bag has only r red marbles and b blue marbles. If five red marbles

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Math Expert
Joined: 02 Sep 2009
Posts: 51215
A bag has only r red marbles and b blue marbles. If five red marbles  [#permalink]

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25 Jul 2018, 23:16
00:00

Difficulty:

5% (low)

Question Stats:

87% (00:39) correct 13% (01:00) wrong based on 54 sessions

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A bag has only r red marbles and b blue marbles. If five red marbles and one blue marble are added to the bag, and if one marble is then selected at random from the bag, then the probability that the marble selected will be blue is represented by

A. b/r

B. b/(b + r)

C. (b + 1)/(r + 5)

D. (b + 1)/(r + b + 5)

E. (b + 1)/(r + b + 6)

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Re: A bag has only r red marbles and b blue marbles. If five red marbles  [#permalink]

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25 Jul 2018, 23:20
Number of red marbles = r

Number of blue marbles = b

five red marbles and one blue marble are added to the bag

Number of red marbles = r + 5

Number of blue marbles = b + 1

Total number of marbles = r + 5 + b + 1 = r + b + 6

Probability of selecting a blue marbles = $$\frac{b + 1}{r + b + 6}$$

Hence option E
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Re: A bag has only r red marbles and b blue marbles. If five red marbles  [#permalink]

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26 Jul 2018, 01:02
Bunuel wrote:
A bag has only r red marbles and b blue marbles. If five red marbles and one blue marble are added to the bag, and if one marble is then selected at random from the bag, then the probability that the marble selected will be blue is represented by

A. b/r

B. b/(b + r)

C. (b + 1)/(r + 5)

D. (b + 1)/(r + b + 5)

E. (b + 1)/(r + b + 6)

Red marbles = r

Blue marbles = b

Changing Situation :

Red = r + 5

Blue = b + 1

Total = r + s + 6

we are asked to pick up a blue marbles = $$\frac{( b + 1)}{r + s + 6}$$

Thus the best answer is E.
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Re: A bag has only r red marbles and b blue marbles. If five red marbles  [#permalink]

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30 Jul 2018, 10:51
Bunuel wrote:
A bag has only r red marbles and b blue marbles. If five red marbles and one blue marble are added to the bag, and if one marble is then selected at random from the bag, then the probability that the marble selected will be blue is represented by

A. b/r

B. b/(b + r)

C. (b + 1)/(r + 5)

D. (b + 1)/(r + b + 5)

E. (b + 1)/(r + b + 6)

After 5 red marbles and 1 blue marble are added to the bag, the bag has b + 1 blue marbles and r + b + 5 + 1 = r + b + 6 total marbles. So the probability of selecting a blue marble is (b + 1)/(b + r + 6).

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Re: A bag has only r red marbles and b blue marbles. If five red marbles &nbs [#permalink] 30 Jul 2018, 10:51
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