Hard q's FOR ME

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golu23: Senior | Next Rank: 100 Posts; Posts: 54; Joined: Sat Jul 09, 2011 5:34 pmFollowed by: 1 member; Thanked: 1 times

by golu23 » Sat Nov 26, 2011 11:13 pm

1)The avg and std deviation of a certain normal distribution are 13.5 &1.5 resp.
What vallue is exactly 2 std deviation lessthan the mean?
a)10.5 b)11.0 c)11.5 d)12.0 e)12.5

2) The area of a square garden is "A" sqft & perimtr is P.iF A=2p+9 P=?
A)28 B)36 c)40 d)56 e)64

7)jOHUA AND jOSE WORK AT auto repaie shop along with 4 others.
What is the probablity the J
oshua and jose will be chosen for a programme
a)1/15 b)1/12 c)1/9 d)1/6 e)1/3

Please with me with these questions especially the first one.

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Source: Beat The GMAT — Problem Solving | Sat Nov 26, 2011 11:13 pm

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Sat Nov 26, 2011 11:17 pm

golu23 wrote:1)The avg and std deviation of a certain normal distribution are 13.5 &1.5 resp.
What vallue is exactly 2 std deviation lessthan the mean?
a)10.5 b)11.0 c)11.5 d)12.0 e)12.5

Please with me with these questions especially the first one.

Given Average = Mean = 13.5

SD = 1.5 -> 2*S.D = 3

2S.D less than mean = 13.5-3 = 10.5 A IMO

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shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Sat Nov 26, 2011 11:23 pm

golu23 wrote:
2) The area of a square garden is "A" sqft & perimtr is P.iF A=2p+9 P=?
A)28 B)36 c)40 d)56 e)64

Let the side of the square be 'a' units;

Given area = A = a^2 and Perimeter P = 4a

GIven, a^2 = 2*(4a) + 9

-> a^2 - 8a - 9 =0

a = 9 (or) a = -1 (side cannot be -ve). Hence side = 9

Perimeter = 4*9 = 36 B IMO.

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[email protected]: Junior | Next Rank: 30 Posts; Posts: 21; Joined: Mon Oct 10, 2011 12:15 amFollowed by: 1 member; Location: India; Thanked: 4 times

by [email protected] » Sun Nov 27, 2011 3:48 am

1) As we need to fin d number 2 std deviation less then mean and each SD is equal to 1.5 so answer would be 13.5-3 = 10.5

Ashish

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Mon Nov 28, 2011 9:57 pm

Joshua and Jose work at auto repair shop along with 4 others. What is the probablity that Joshua and Jose will be chosen for a programme?
a)1/15 b)1/12 c)1/9 d)1/6 e)1/3

Total people = 6
Probability that the 1st person chosen is Joshua or Jose = 2/6
Probability that the next one chosen is Joshua or Jose = 1/5 (since a is chosen so out of 6, 5 people are left)
Probability that Joshua and Jose will both be chosen = 2/6 * 1/5 = [spoiler]1/15[/spoiler]

The correct answer is A.

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chieftang: Master | Next Rank: 500 Posts; Posts: 218; Joined: Wed Nov 23, 2011 8:05 pmFollowed by: 4 members; Thanked: 26 times

by chieftang » Tue Nov 29, 2011 12:03 am

golu23 wrote:1)The avg and std deviation of a certain normal distribution are 13.5 &1.5 resp.
What vallue is exactly 2 std deviation lessthan the mean?
a)10.5 b)11.0 c)11.5 d)12.0 e)12.5

2) The area of a square garden is "A" sqft & perimtr is P.iF A=2p+9 P=?
A)28 B)36 c)40 d)56 e)64

1. 13.5 - (1.5*2) = 10.5

2. P = 4 * sqrt(2P+9)
P^2 = 16(2P+9)
P^2 = 32P + 144
P^2 - 32P - 144 = 0
(P - 36)(P + 4) = 0
P = 36, -4 (discard -4)
P is 36

3. Sounded like 1/3 * 1/5 = 1/15

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