case study on two friends

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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 » Thu Oct 08, 2015 2:44 am

A case study on two friends Sarah and Christie revealed that c years ago Sarah was half as old as what Christie will be in s years from now. The study also revealed that s years ago Sarah was 2 fewer than half as old as what Christie will be in c years from now. If Christie’s present age is 36, what is the value of s – c?
A. 2
B. 4
C. 5
D. 7
E. It cannot be determined from the information given

[spoiler]Made Up!

Answer: B. 4[/spoiler]

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Source: Beat The GMAT — Problem Solving | Thu Oct 08, 2015 2:44 am

theCEO: Master | Next Rank: 500 Posts; Posts: 363; Joined: Sun Oct 17, 2010 3:24 pmFollowed by: 3 members; Thanked: 115 times

by theCEO » Sat Oct 10, 2015 3:05 am

sanju09 wrote:A case study on two friends Sarah and Christie revealed that c years ago Sarah was half as old as what Christie will be in s years from now. The study also revealed that s years ago Sarah was 2 fewer than half as old as what Christie will be in c years from now. If Christie’s present age is 36, what is the value of s – c?
A. 2
B. 4
C. 5
D. 7
E. It cannot be determined from the information given

[spoiler]Made Up!

Answer: B. 4[/spoiler]

Sa = Sarah and Ch = Christie

Sa-c = 0.5(Ch+s) ->equation1
Sa-s = 0.5(Ch+c)-2 ->equation 2

equation1 - equation 2

-c-(-s)= 0.5s - 0.5c +2
-c+s = 0.5s - 0.5c +2
-c + 0.5c + s - 0.5s = 2
-0.5c + 0.5s = 2
-c + s = 4
s - c = 4

ans = b

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