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This is more about the relative scale of the quantities than anything. It's easier to think about it with numbers you can picture, so assume you have an equation like 1 000 000 000 (10^7) - 100 (10^2). This equation can still be approximated as 10^7, since the latter term is so insignificantly small compared to the former term.

Re: GMAT, Number Properties, Exponents [#permalink]
17 Jan 2012, 14:27

Expert's post

Baten80 wrote:

I found the answer options are: a. 10^210 b. 10^180 c. 10^150 d. 10^90 e. 10^6

I answered B. What is correct?

10^180 - 10^30 = Which of the following best approximates the value of the expression above?

Yes, answer 10^180 is correct. Note that we need approximate value of the given expression and as 10^(180) is much larger number than 10^(30) then 10^(30) is pretty much negligible in this case: 10^(180)-10^(30)=~10^(180).

Re: GMAT, Number Properties, Exponents [#permalink]
08 Jul 2013, 17:25

Bunuel wrote:

Baten80 wrote:

I found the answer options are: a. 10^210 b. 10^180 c. 10^150 d. 10^90 e. 10^6

I answered B. What is correct?

10^180 - 10^30 = Which of the following best approximates the value of the expression above?

Yes, answer 10^180 is correct. Note that we need approximate value of the given expression and as 10^(180) is much larger number than 10^(30) then 10^(30) is pretty much negligible in this case: 10^(180)-10^(30)=~10^(180).

Re: GMAT, Number Properties, Exponents [#permalink]
08 Jul 2013, 22:09

1

This post received KUDOS

Expert's post

cumulonimbus wrote:

Bunuel wrote:

Baten80 wrote:

I found the answer options are: a. 10^210 b. 10^180 c. 10^150 d. 10^90 e. 10^6

I answered B. What is correct?

10^180 - 10^30 = Which of the following best approximates the value of the expression above?

Yes, answer 10^180 is correct. Note that we need approximate value of the given expression and as 10^(180) is much larger number than 10^(30) then 10^(30) is pretty much negligible in this case: 10^(180)-10^(30)=~10^(180).

Re: GMAT, Number Properties, Exponents [#permalink]
08 Jul 2013, 23:27

cumulonimbus wrote:

Bunuel wrote:

Baten80 wrote:

I found the answer options are: a. 10^210 b. 10^180 c. 10^150 d. 10^90 e. 10^6

I answered B. What is correct?

10^180 - 10^30 = Which of the following best approximates the value of the expression above?

Yes, answer 10^180 is correct. Note that we need approximate value of the given expression and as 10^(180) is much larger number than 10^(30) then 10^(30) is pretty much negligible in this case: 10^(180)-10^(30)=~10^(180).

Hi Bunnel, Their are two sets of options on this page. How to decide b/w 10^180 and 10^179.

Hi cumulonimbus

I think 10^180 is closer. Because 1 is very small, 10^x - 1 is closer to 10^x than 10^(x-1).

Let try few examples, you can see the pattern. 10^2 - 1= 99 ==> closer to 10^2 = 100 than 10^1 = 10 10^3 - 1 = 999 ==> closer to 10^3 = 1000 than 10^2 = 100 10^4 - 1 = 9999 ===> closer to 10^4 = 10000 than 10^3 = 1000 ..... 10^180 - 1 ==> closer to 10^180 than 10^179

Hope it helps. _________________

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Re: 10^180-10^30. Which of the following best approximates [#permalink]
27 Feb 2015, 09:56

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Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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