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Taking GMAT Tomorrow - NEED HELP WITH A FEW PROBLEMS [#permalink]
23 Jun 2008, 13:21

Hi All!

I am taking the GMAT tomorrow .

I'm doing fine with on the "harder" MGMAT quant questions but am running into some small "simple" problems on the GMAT Prep that are hurting my score.

Please provide explanations for the following:

1. If (1/5)^m * (1/4)^18 = 1/[(2)(10)^35], what is the value of m?

The answer is m=35. Please tell me why.

2. What is the value of 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8?

The answer is 2^9. I can find the answer by doing the long work but would like to know if someone knows a fast way to do it.

3. The mass of 1 cubic meter of a substance is 800 kg under certain conditions. What is the volume in cubic centimeters of 1 gram of this substance under these conditions? (NOTE: 1kg = 1,000 grams and 1 cubic meter = 1,000,000 cubic centimeters)

The answer is 1.25. I admittedly suck at conversions. Please help!

3. The mass of 1 cubic meter of a substance is 800 kg under certain conditions. What is the volume in cubic centimeters of 1 gram of this substance under these conditions? (NOTE: 1kg = 1,000 grams and 1 cubic meter = 1,000,000 cubic centimeters)

The answer is 1.25. I admittedly suck at conversions. Please help![/quote]

1 cubic meter = 1,000,000 cubic centimeters; 800 kg = 800,000 grams 1,000,000 cubic centimeters / 800,000 grams = 1.25 cubic centimeters / 1.25 grams (divide 1,000,000 by 800,000)

2. What is the value of 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8? This is a GP series a + ar + ar^2 + ar^3 + ... Sum of GP Series = a (1-r^n)/(1-r) Where a is first term, r is common factor between each successive terms and n is number of terms. In this case we have a = 1, r = 2, n = 9 (I think your series start with 2^0 or 1 and not 2) So Sum = 1 * (1 - 2^9) / (1-2) = 2^9 (approximately, 1 is too small in comparison to 2^9)

The answer is 2^9. I can find the answer by doing the long work but would like to know if someone knows a fast way to do it.

3. The mass of 1 cubic meter of a substance is 800 kg under certain conditions. What is the volume in cubic centimeters of 1 gram of this substance under these conditions? (NOTE: 1kg = 1,000 grams and 1 cubic meter = 1,000,000 cubic centimeters)

Re: Taking GMAT Tomorrow - NEED HELP WITH A FEW PROBLEMS [#permalink]
24 Jun 2008, 03:24

abhijit_sen wrote:

2. What is the value of 2 + 2 + 2^2 + 2^3 + 2^4 + 2^5 + 2^6 + 2^7 + 2^8? This is a GP series a + ar + ar^2 + ar^3 + ... Sum of GP Series = a (1-r^n)/(1-r) Where a is first term, r is common factor between each successive terms and n is number of terms. In this case we have a = 1, r = 2, n = 9 (I think your series start with 2^0 or 1 and not 2) So Sum = 1 * (1 - 2^9) / (1-2) = 2^9 (approximately, 1 is too small in comparison to 2^9)

There is no approximation.

The formula is in fact 1 + r + r^2 + r^3 + ... + r^n = \frac{1-r^n^+^1}{1-r}