5 to each

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Wed May 19, 2010 4:35 am

The mean of a data set is equal to 10 and its standard deviation is equal to 1. If we add 5 to each data value, then the mean and standard deviation would respectively become
(A) 10 & 1
(B) 10 & 6
(C) 15 & 1
(D) 15 & 6
(E) 10 & 15

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Source: Beat The GMAT — Problem Solving | Wed May 19, 2010 4:35 am

liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Wed May 19, 2010 4:40 am

mean will be 10+5=15 and sd will be same 1

Ans option C

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Wed May 19, 2010 4:44 am

liferocks wrote:mean will be 10+5=15 and sd will be same 1

Ans option C

Why does the SD not change here?

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

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pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Wed May 19, 2010 4:44 am

imo C is answer

s.d is deviation from mean of the variables. when variable changes with certain amount the mean will change with same amount hence the deviation of variable from means will remain same.

e.g 9 and 11 means is 10 and s.d =1 devaitions 9-10=-1 and 11-10=1

when 5 is added 14 and 16 means = 15 deviations 14-15=-1 and 16-15=1 hence s.d = 1

i hope it helps

Last edited by pradeepkaushal9518 on Wed May 19, 2010 4:49 am, edited 1 time in total.

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liferocks: Legendary Member; Posts: 576; Joined: Sat Mar 13, 2010 8:31 pmFollowed by: 1 member; Thanked: 97 times

by liferocks » Wed May 19, 2010 4:47 am

sd is the deviation of value from mean..since both mean and the value is increased by 5..relative change is 0..hence change in sd 0

"If you don't know where you are going, any road will get you there."
Lewis Carroll

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