GMAT symbolism

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Lynn0423: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sun Apr 01, 2007 3:51 pm

by Lynn0423 » Sun Apr 01, 2007 4:02 pm

Hello: I;m posting again as I think I posted in the wrong forum.

I encountered a question regarding GMAT symbolism which has me scratching my head a little. The question is:

~x=(x^2+1)/2 ; ~y=3y/2 for all integers x and y. If m=2, ~m is equal to which of the following:

A. 13/8
B. 3
C. 15/4
D. 5
E. 37/2

The answer is D.

for ~x, x is in a cirled and for ~y, y is in a box. For ~m, m is in a box and a circle.

Thanks!

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Source: Beat The GMAT — Problem Solving | Sun Apr 01, 2007 4:02 pm

Prasanna: Master | Next Rank: 500 Posts; Posts: 418; Joined: Mon Feb 26, 2007 6:41 pm; Thanked: 24 times

by Prasanna » Sun Apr 01, 2007 5:21 pm

I am not able to follow the question (and the answer). Can any one please help?

Prasanna

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jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

by jayhawk2001 » Sun Apr 01, 2007 6:47 pm

If I understand the question correctly, we have to compute
~2 based on formula for ~y and then use the result in ~x

So, we have

~2 = 3*2/2 = 3

Using this in ~x, we have (3^2 + 1) / 2 = 5

If you have a snapshot (pictorial representation) of the question,
please send so that we can confirm

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Lynn0423: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sun Apr 01, 2007 3:51 pm

by Lynn0423 » Sun Apr 01, 2007 8:44 pm

Jay,

Sorry, call me thick, but if you put x as equal to 2, solve then sub in for y the equation does not calculate (following the same logic just solving for x first). I don't get it. How does one know when to solve for y first and then x or vice versa? I simply cannot follow your logic.

L.

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ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

Re: GMAT symbolism

by ajith » Sun Apr 01, 2007 8:47 pm

Lynn0423 wrote:Hello: I;m posting again as I think I posted in the wrong forum.

I encountered a question regarding GMAT symbolism which has me scratching my head a little. The question is:

~x=(x^2+1)/2 ; ~y=3y/2 for all integers x and y. If m=2, ~m is equal to which of the following:

A. 13/8
B. 3
C. 15/4
D. 5
E. 37/2

The answer is D.

for ~x, x is in a cirled and for ~y, y is in a box. For ~m, m is in a box and a circle.

Thanks!

Let me re-phase the question to a more mathematical form

f(x) = (x^2+1)/2
g(x) = 3*x/2

Now they are asking for f (g(2))

for this

g(2) = 2*3/2 =3

f(g(2) = f(3) = (3^2+1)/2 =10/2 =5

Always borrow money from a pessimist, he doesn't expect to be paid back.

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ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Sun Apr 01, 2007 8:59 pm

Lynn0423 wrote:Jay,

How does one know when to solve for y first and then x or vice versa? I simply cannot follow your logic.

L.

That depends on whether
a) 2 is in the circle enclosed by the box
b) 2 is in the box enclosed by circle

do the innermost operation first

I will explain in case of a

Do the operation curresponding to circle first because that is inner
Do the outer operation next on the result of first operation.

is it clear?

Always borrow money from a pessimist, he doesn't expect to be paid back.

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Lynn0423: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sun Apr 01, 2007 3:51 pm

by Lynn0423 » Sun Apr 01, 2007 9:25 pm

Ajith, thanks!! I got it! Now I remember the rules of those operations! Thanks. BTW, that question was from Kaplan course book 2006-2007.

Thanks again for your help!

L.

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Cybermusings: Legendary Member; Posts: 559; Joined: Tue Mar 27, 2007 1:29 amFollowed by: 2 members; Thanked: 5 times

by Cybermusings » Mon Apr 02, 2007 3:48 am

This one seems simple enough. m is in a circle in a square.

Thus you first have to perform the function of a circle and then the square

Function in a circle = (x^2+1)/2 ; for any integer x

Thus for m=2 it equals (2^2 + 1)/2 = 5/2

Now perform the function of a square

Function in a square = (3y/2)

= 3/2 * 5/2 = 15/4

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