gmat prep PS

[guest]

of 800 employees of company X, 70% have been with the company at least 10 years. if y of these long term members were to retire and no other employee changes were to occur, what value of y would reduce the percent of the long term employees in th ecompany to 60%?

a 200
b 160
c 112
d 80
e 56

can someone post an explanation please? thank you

[sheetal]

# of employee with atleast 10 years service = (0.7) x (800) = 560

[(560 - y)/800 ] * 100 = 60

=> y = 80
D is the ans

[guest]

actually GMAT prep lists the answer as being A..200. how is that possible? did anyone else get this question on their exam? i thought the answer was 80.

[Vasu]

If y employees having 10 or more yrs of service are to retire, The total number of employees which is currently 800, will also come down by the same number. The remaining 10 yr service employees should contribute to 60% of the total employee strength. Therefore,

560-y=60% of (800-y)
=> 560-y=0.6(800-y)
=> 560-y=480-0.6y
=> y=80/0.4
=> y=200 Answer

[StaceyKoprince]

Nice, vasu. Looks like the guest and sheetal made the same calculation error, which was to forget to reduce the total number of employees (800) by y in the calculation. Notice that they know what errors we are most likely to make and those errors are built right into the answer choices! So annoying!

[guest]

well also i think they word things badly...they dont make it clear that they want 60% of the remaining employees...i was thinking 60% of the original 800 employees...

[RonPurewal]

well also i think they word things badly...they dont make it clear that they want 60% of the remaining employees...i was thinking 60% of the original 800 employees...

a couple of comments here:

* that's actually the only reasonable interpretation of the wording. here's an analogy to show that the alternative interpretation (= % of the original number) doesn't make sense: imagine that a school originally has 50 boys and 50 girls, so that its student body is 50% girls. now, let's say all the boys leave, and 10 girls leave as well, so that only 40 girls (and no boys) are left.
would you now say that the percentage of girls at the school is 40% (= 40/100)? no, of course you wouldn't; it's now 100%, because you have to divide by the current total. you can never calculate a percentage by dividing a current portion by a previous total. while i wouldn't expect you to come up with analogies such as this one on the fly, you may want to try to think in terms of such analogies if you ever find yourself questioning the wording of a problem.

* i understand that being caught misinterpreting answer choices like this one is frustrating - it's the same way i feel when i totally misconstrue something said to me in a foreign language. however, try to parlay that frustration into a better understanding of the 'language' spoken by your interlocutor (which in this case is the gmat). in other words, you should try to learn the way the gmat words its problems. it has a special, super-precise 'dialect' all its own, which you would be extremely well advised to get used to.