A jar contains 16 marbles, of which 4 are red, 3 are blue, and the res

Question

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the rest are yellow. If 2 marbles are to be selected at random from the jar, one at a time without being replaced, what is the probability that the first marble selected will be red and the second marble selected will be blue?

A. 3/64
B. 1/20
C. 1/16
D. 1/12
E. 1/8

A. 3/64
B. 1/20
C. 1/16
D. 1/12
E. 1/8

Bunuel · Answer

Note that we want  the first  marble selected to be red and  the second  marble selected to be blue.

P=4/16*3/15=1/20.

Answer: B.

gmatpapa · Answer

Its an "and" question so think multiplication.

Let P{a}= P{1st marble is red}=  \frac{4}{16} 
P{B}=P{2nd marble is blue}= \frac{3}{15}

P{A}andp{B}= \frac{4}{16}*\frac{3}{15}= \frac{1}{20}

Answer B.

banksy · Answer

gmatpapa, if we have "and" so it is multiplication, and if "or" it means addition?

gmatpapa · Answer

When you are determining the probability of one event AND another event, multiply the two probabilities together. Add the probabilities if you are determining the probability of one event OR another another event.

Example. The probabilities of chip and dale scoring 700 on GMAT are 1/10 and 1/15 respectively. What is the probability that:

1. Both Chip AND Dale score a 700: Since this is an AND question, you multiply them together. Therefore, 
P{both score 700}=  \frac{1}{10}*\frac{1}{15}=\frac{1}{150}

2. Either Chip OR Dale scores a 700: P{Chip scores 700}+P{Dale scores 700}-P{both score 700}=  \frac{1}{10}+\frac{1}{15}-\frac{1}{150}= \frac{12}{75} .

fitzpratik · Answer

Total Marbles = 16

R=4
B=3
Y=9

First is red  AND   second is blue  without replacement

to choose first red marble: can be chosen in 4/16 ways, OR  1/4  ways

Now choose second marble  without replacement  that has to be blue, which can be chosen in 3/15 {3 blue balls, and ONE red ball is already chosen, and not replaced} ways. 3/15 =  1/5

The complete probability of the event (First is red  AND   second is blue  without replacement )

(1/4)*(1/20)

1/20

B

gmatdordie · Answer

total ways of selecting marbles=16
Total ways of selecting Red marble=4/16
As marbles are not replaced
so ways of selecting blue marble=3/15
so Total prob=4/16 * 3/15=1/4 * 1/5=1/20

bumpbot · Answer

Automated notice from GMAT Club BumpBot: 

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

 This post was generated automatically.

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the res

Prep Toolkit

Top 5 GMAT Debrief Videos

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

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the res

Prep Toolkit

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

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards