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A certain board game consists of a circular path of 100 spaces colored in a repeating pattern of black, yellow, green, red and blue. what is the probability that, in a random selection of seven consecutive spaces, 2 of the spaces are blue?
A. 2/25
B. 1/7
C. 1/5
D. 2/7
E. 2/5
A. 2/25
B. 1/7
C. 1/5
D. 2/7
E. 2/5
07 Mar 2011, 02:49
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Moved to PS subforum.
We have a pattern of 5 colors: black - yellow - green - red - blue. To have 2 blue spaces in a string of 7 spaces the starting space must be either blue or red (in I case: first and sixth spaces will be blue and in the II case: second and seventh spaces will be blue). The probability that the starting space will be either blue or red is 2/5.
Answer: E.
P.S. Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/
and DS questions in the DS subforum: gmat-data-sufficiency-ds-141/ No posting of PS/DS questions is allowed in the main Math forum.
akriti13
a certain board game consists of a circular path of 100 spaces colored in a repeating pattern of black, yellow, green, red and blue. what is the probability that, in a random selection of seven consecutive spaces, 2 of the spaces are blue?
a)2/25
b)1/7
c)1/5
d)2/7
e)2/5
a)2/25
b)1/7
c)1/5
d)2/7
e)2/5
We have a pattern of 5 colors: black - yellow - green - red - blue. To have 2 blue spaces in a string of 7 spaces the starting space must be either blue or red (in I case: first and sixth spaces will be blue and in the II case: second and seventh spaces will be blue). The probability that the starting space will be either blue or red is 2/5.
Answer: E.
P.S. Please post PS questions in the PS subforum: gmat-problem-solving-ps-140/
and DS questions in the DS subforum: gmat-data-sufficiency-ds-141/ No posting of PS/DS questions is allowed in the main Math forum.
General Discussion
07 Mar 2011, 03:05
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Ans: "E"
There are 100 possible ways to select 7 consecutive spaces.
1-7
2-8
3-9
4-10
.
.
98-104
99-105
100-106
Let's fix the first colored space as Black; Representing Black as K and blue as B.
KYGRBKYGRBKYGRBKYGRB... 20 SUCH GROUPS
How to get 2 blues.
KYG[R{BKYGRB]K}YGRBKYGRB
If the starting space is Red and last space Blue; positions will be; 4,9,14,19,....94,99= count 20
OR
If the starting space is Blue and last space Black; positions will be; 5,10,15,20...95,100= count 20
20+20=40
There are 40 favorable ways.
P=40/100=2/5
Ans: "E"
There are 100 possible ways to select 7 consecutive spaces.
1-7
2-8
3-9
4-10
.
.
98-104
99-105
100-106
Let's fix the first colored space as Black; Representing Black as K and blue as B.
KYGRBKYGRBKYGRBKYGRB... 20 SUCH GROUPS
How to get 2 blues.
KYG[R{BKYGRB]K}YGRBKYGRB
If the starting space is Red and last space Blue; positions will be; 4,9,14,19,....94,99= count 20
OR
If the starting space is Blue and last space Black; positions will be; 5,10,15,20...95,100= count 20
20+20=40
There are 40 favorable ways.
P=40/100=2/5
Ans: "E"
