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#### Manhattan GMAT chapter 11 q11

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 Post subject: Manhattan GMAT chapter 11 q11  Posted: Tue Feb 28, 2012 12:17 am
 Students

Posts: 11
 A machinist's salary increases by \$2000 at the end of each full year the machinist works. If his salary for the fifth year is 39000. What is the machinist's average annual salary for his first 21 years at the factory?I tried setting this up and got an answer that was not close.Here is what I did :Y= salary at the beginning of year 1.x= Number of years = given as 21.Fifth year salary = y + 4(2000)=39000( used 4 above since the question says that the salary for the fifth year - rather than the salary at the end of year 5).y= 31000Avg amount of money earned in 21 years :((31000)21 + 2000(21))/21 = 33,000 ( after the end of 21 years)The answer given is 51000.The answer is derived by using the properties of evenly spaced sets -- Have I misunderstood the question?

 Post subject: Re: Manhattan GMAT chapter 11 q11  Posted: Tue Feb 28, 2012 2:03 pm
 Students

Posts: 39
 Hey Ayush,Notice following mistake in your calculation :Average Salary= Sum of 21 years salary/21But Sum of 21 years salary is not equal to 31000*21+2000*21 as you have used.Instead as you can see, the sum will be 31000*21 + 2000 (for the second year) + 2000*2 (for third year) + 2000*3 (for fourth year) + ...2000*20 ( for 21st year) = 31000*21 + 2000* (1+2+3+4+...20) = 31000*21 + 2000* (20*21/2)= 31000*21+2000*210So Average= 31000+20000=51000Hope it is clear.NK

 Post subject: Re: Manhattan GMAT chapter 11 q11  Posted: Wed Feb 29, 2012 10:36 pm
 Students

Posts: 11
 thanks man -- that really helped :)

 Post subject: Re: Manhattan GMAT chapter 11 q11  Posted: Sun Mar 11, 2012 11:20 pm
 ManhattanGMAT Staff

Posts: 2391
 LazyNK strikes again! Thanks so much! :-) _________________Jamie NelsonManhattanGMAT Instructor

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