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GMATDUD: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue Jan 16, 2007 9:40 am; Location: Arlington,VA

Math DS

by GMATDUD » Fri Feb 08, 2008 10:02 am

Hi ,

Can someone help me with this... Its a real simple question , but I am still confused . The concept of rounding GMAC follows is not what I leart in my math classes...

For Ex: round ..4545 to the nearest hundredth - = .46 . IS what I did correct ?

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Source: Beat The GMAT — Data Sufficiency | Fri Feb 08, 2008 10:02 am

its_me07: Senior | Next Rank: 100 Posts; Posts: 83; Joined: Mon Oct 22, 2007 4:44 am; Thanked: 1 times

by its_me07 » Fri Feb 08, 2008 11:15 am

is the OA a?

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GMATDUD: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue Jan 16, 2007 9:40 am; Location: Arlington,VA

by GMATDUD » Fri Feb 08, 2008 4:34 pm

OA is C

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Fri Feb 08, 2008 9:48 pm

When possible, please type out the question instead of posting a link. Makes it much easier to respond.

Q: what is the result when X is rounded to the nearest hundredth?

(1) when x is rounded to the nearest thousandth, the result is .455

let's pick x = .4546 If we round to the nearest hundredth we get .45

let's pick x = .4554 If we round to the nearest hundredth we get .46

Two possible answers, therefore (1) is insufficient.

(2) the thousandths digit of x is 5

We have no clue what the hundredths digit is, so (2) is insufficient.

Let's try together:

We know that roudned off our number is .455 and we know that the thousandths digit is 5.

So, we could have started with:

.4550
.4551
.4552
.4553
.4554

For all 5 of those possibilities, if we round to the nearest hundredth, we get .46

Together the statements lead to only one answer, so they're sufficient: choose (c).

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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GMATDUD: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue Jan 16, 2007 9:40 am; Location: Arlington,VA

by GMATDUD » Fri Feb 08, 2008 11:37 pm

Stuart ,

Thanks for responding .. I have an additional question for you .

in the example you stated : .4546 ... If I had to round to the nearest hundred , wont it be 0.46. My understanding was u start at the last digit and round your way back up . That being said , my logic was

0.4546 --> 0.0455 --0.046

Do I make any sense ? I could have my fundamentals wrong and I would appreciate if you can help me out.

Thanks for your response. I was hoping you respond.

cheers,
T

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arawamis: Junior | Next Rank: 30 Posts; Posts: 15; Joined: Tue Sep 25, 2007 7:02 pm; Thanked: 4 times

by arawamis » Sat Feb 09, 2008 12:36 pm

what about rounding 0.456 to units digit? does it go like this 0.456 -> 0.46 -> 0.5 -> 1???

Stuart Kovinsky wrote:When possible, please type out the question instead of posting a link. Makes it much easier to respond.

Q: what is the result when X is rounded to the nearest hundredth?

(1) when x is rounded to the nearest thousandth, the result is .455

let's pick x = .4546 If we round to the nearest hundredth we get .45

let's pick x = .4554 If we round to the nearest hundredth we get .46

Two possible answers, therefore (1) is insufficient.

(2) the thousandths digit of x is 5

We have no clue what the hundredths digit is, so (2) is insufficient.

Let's try together:

We know that roudned off our number is .455 and we know that the thousandths digit is 5.

So, we could have started with:

.4550
.4551
.4552
.4553
.4554

For all 5 of those possibilities, if we round to the nearest hundredth, we get .46

Together the statements lead to only one answer, so they're sufficient: choose (c).

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GMATDUD: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Tue Jan 16, 2007 9:40 am; Location: Arlington,VA

by GMATDUD » Sat Feb 09, 2008 12:42 pm

Arawamis ,

That would be my understanding.

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Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Sat Feb 09, 2008 2:57 pm

You round off based on as much information as you have.

So, if we're rounding .4546 to the nearest hundredth, we're 46/100 points between .45 and .46. Since we're less than halfway there, we round down (to .45).

In general, we don't do double (or triple) rounding - we use all the info at our disposal.

So, .456 is 456/1000 of the distance between 0 and 1. 456 is less than 1/2 of 1000, so we'd round down to 0.

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aj5105: Legendary Member; Posts: 1169; Joined: Sun Jul 06, 2008 2:34 am; Thanked: 25 times; Followed by:1 members

by aj5105 » Fri Jan 16, 2009 9:27 am

neat explanation Stuart !

Stuart Kovinsky wrote:When possible, please type out the question instead of posting a link. Makes it much easier to respond.

Q: what is the result when X is rounded to the nearest hundredth?

(1) when x is rounded to the nearest thousandth, the result is .455

let's pick x = .4546 If we round to the nearest hundredth we get .45

let's pick x = .4554 If we round to the nearest hundredth we get .46

Two possible answers, therefore (1) is insufficient.

(2) the thousandths digit of x is 5

We have no clue what the hundredths digit is, so (2) is insufficient.

Let's try together:

We know that roudned off our number is .455 and we know that the thousandths digit is 5.

So, we could have started with:

.4550
.4551
.4552
.4553
.4554

For all 5 of those possibilities, if we round to the nearest hundredth, we get .46

Together the statements lead to only one answer, so they're sufficient: choose (c).

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CJCG: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Thu Jul 08, 2010 2:51 am

by CJCG » Sat Jul 10, 2010 12:11 am

Hi Stuart,

Thanks for your help. I have a doubt regarding what you explained.

You end up with a list of numbers which is as follows:

.4550
.4551
.4552
.4553
.4554

And you say that "For all 5 of those possibilities, if we round to the nearest hundredth, we get .46". Actually .4550 is as close to .45 as to .46... why do we assume that it should be rounded to .46 instead of .45?

Many thanks!

Pablo

Stuart Kovinsky wrote:When possible, please type out the question instead of posting a link. Makes it much easier to respond.

Q: what is the result when X is rounded to the nearest hundredth?

(1) when x is rounded to the nearest thousandth, the result is .455

let's pick x = .4546 If we round to the nearest hundredth we get .45

let's pick x = .4554 If we round to the nearest hundredth we get .46

Two possible answers, therefore (1) is insufficient.

(2) the thousandths digit of x is 5

We have no clue what the hundredths digit is, so (2) is insufficient.

Let's try together:

We know that roudned off our number is .455 and we know that the thousandths digit is 5.

So, we could have started with:

.4550
.4551
.4552
.4553
.4554

For all 5 of those possibilities, if we round to the nearest hundredth, we get .46

Together the statements lead to only one answer, so they're sufficient: choose (c).

Quote

Testluv: GMAT Instructor; Posts: 1302; Joined: Mon Oct 19, 2009 2:13 pm; Location: Toronto; Thanked: 539 times; Followed by:164 members; GMAT Score:800

by Testluv » Sat Jul 10, 2010 2:21 am

And you say that "For all 5 of those possibilities, if we round to the nearest hundredth, we get .46". Actually .4550 is as close to .45 as to .46... why do we assume that it should be rounded to .46 instead of .45?

...for the same reason that we round 0.5 to 1 rather than to 0 (even though 0.5 is as close to 1 as it is to 0).

Kaplan Teacher in Toronto

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CJCG: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Thu Jul 08, 2010 2:51 am

by CJCG » Sat Jul 10, 2010 7:47 am

Testluv wrote:
And you say that "For all 5 of those possibilities, if we round to the nearest hundredth, we get .46". Actually .4550 is as close to .45 as to .46... why do we assume that it should be rounded to .46 instead of .45?
...for the same reason that we round 0.5 to 1 rather than to 0 (even though 0.5 is as close to 1 as it is to 0).

So basically whenever we have a decimal that is as close to one as to the other we should round up. Is that correct, Testluv?

Many thanks!

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Testluv: GMAT Instructor; Posts: 1302; Joined: Mon Oct 19, 2009 2:13 pm; Location: Toronto; Thanked: 539 times; Followed by:164 members; GMAT Score:800