very simple task

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Lattefah84: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Mon Dec 14, 2009 4:15 am

by Lattefah84 » Fri Dec 18, 2009 4:53 am

This is a very simple task, but when I checked the results, I realized that I probably missed something.

If x=-1
y=-2
z=4

Find the value of (x-2)/5y + z

My way :

(-1-2)/5*(-2) + 4 = -3/-10 + 4 = 3/10 + 4 = 3 + 40/ 10 = 43/10 = 4 3/10 (four and three tenths)

Book:

(-1-2)/5(-2) + 4 = -3/5* -2 + 4 = 6/5 + 4 = 6/5 + 20/5 = 26/5 = 5 1/5 (five and one fifth)

It is impossible that -3/5(-2) to write like -3/5 * -2 (-2 in the same plane as -3)

so, I just want to hear that I'm right

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Source: Beat The GMAT — Quantitative Reasoning | Fri Dec 18, 2009 4:53 am

mjsobo: GMAT Instructor; Posts: 27; Joined: Sun Sep 20, 2009 7:54 pm; Thanked: 3 times

by mjsobo » Sun Dec 20, 2009 9:31 pm

hi,
i see the way you did it, but i also see where you might have gone wrong....

if the book has (x-2)/5y + z, then it could also be written as (x-2)/(5)*y + z, which is very different than the way you interpret it as (x-2)/(5y) + z. I'm supposing that the book had the parentheses there for a reason and that is why they didn't have them on the bottom.

In the book's case, (x-2)/5y + z is indeed equal to five and 1/5th, although the way you see it, it is indeed equal to four and three tenths.

it is always good to follow the same format that the book has...in this case, they want only to divide by 5 AND THEN multiply by -2....which could also be written as (x-2)/5*(y)/(1) + z. In this case, i must agree with the book, even though i can agree with how you see it...this is a good moral that parenthesis do matter!!

great question and good luck!

Martin
GMAT Instructor with Grockit

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Lattefah84: Senior | Next Rank: 100 Posts; Posts: 93; Joined: Mon Dec 14, 2009 4:15 am

by Lattefah84 » Mon Dec 21, 2009 4:22 am

But +z is actually apart from the (x-2)/(5y) + z - Z is not under the fraction bar, it is in same level of the fraction bar -so it should be added to result of the fraction , right?

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