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21 Jul 2010, 23:33
Compound Interest
\(Balance(final)=\) \(=principal*(1+\frac{interest}{C})^{time*C}\), where C = the number of times compounded annually.
If C=1, meaning that interest is compounded once a year, then the formula will be: \(Balance(final)=\) \(principal*(1+interest)^{time}\), where time is number of years.
Example: If $20,000 is invested at 12% annual interest, compounded quarterly, what is the balance after 2 year? Solution: \(Balance=20,000*(1+\frac{0.12}{4})^{2*4}=\) \(=20,000*(1.03)^8=25,335.4\)
I dont understand why 0.12/4 ? where did we get no 4 ?
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22 Jul 2010, 04:33
xmagedo wrote: Compound Interest
\(Balance(final)=\) \(=principal*(1+\frac{interest}{C})^{time*C}\), where C = the number of times compounded annually.
If C=1, meaning that interest is compounded once a year, then the formula will be: \(Balance(final)=\) \(principal*(1+interest)^{time}\), where time is number of years.
Example: If $20,000 is invested at 12% annual interest, compounded quarterly, what is the balance after 2 year? Solution: \(Balance=20,000*(1+\frac{0.12}{4})^{2*4}=\) \(=20,000*(1.03)^8=25,335.4\)
I dont understand why 0.12/4 ? where did we get no 4 ?
thanks 12% of annual interest is compounded quarterly, so it's compounded 4 times a year > C=4.
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22 Jul 2010, 07:09
thanks bunnel But one more question, when it says compunded semiannually, does it mean half ? for example 6 ? do we take 3 ? thanks

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02 Aug 2010, 20:59
The Probability material is really helpful thanks...

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06 Aug 2010, 06:47
Thanks for your efforts

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09 Oct 2010, 14:30
Generic questions based on percentages that can be remembered: 1. If the price(p) of an Item increases by x% then consumption(c) has to be decreased by 100 /(100+x) % to keep the expenditure(E) constant. 2. If two articles are sold at same price , and on first one the shopkeeper makes a profit of p% and on the other suffers a loss of p % , overall he suffers a loss. The loss is p*p /100 % ie., ( p square divided by 100). Especially,I have seen the second type of question very common one in many competitive tests. Note : Please let me know if you are interested in the reason behind each answer. This is my first post in gmatclub.I thank all of the gmatclub members / moderators for providing such a wonderful environment.

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23 Oct 2010, 06:32
Hey guys i am new in this forum... can you help me with these percentage problem?
1) The income of a broker remains unchanged though the rate of commission is increased from 4% to 5%. THe percentage slump in business is:
i)1 ii) 8 iii) 20 iv)80
2) p is 6 times as large as q. The percent that q is less than p is:
i) 83.33 ii) 16.5 iii) 90 iv) 60
3) In a market survey 20% voted for A and 60% voted for B. the remaining were uncertain. if the difference between who voted for B and those who were uncertain was 720 how many individuals were covered in the survey?
i) 3600 ii) 1440 iii)1800 iv) cant determine

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23 Oct 2010, 07:21
syenaman wrote: Generic questions based on percentages that can be remembered: 1. If the price(p) of an Item increases by x% then consumption(c) has to be decreased by 100 /(100+x) % to keep the expenditure(E) constant. 2. If two articles are sold at same price , and on first one the shopkeeper makes a profit of p% and on the other suffers a loss of p % , overall he suffers a loss. The loss is p*p /100 % ie., ( p square divided by 100). Especially,I have seen the second type of question very common one in many competitive tests. Note : Please let me know if you are interested in the reason behind each answer. This is my first post in gmatclub.I thank all of the gmatclub members / moderators for providing such a wonderful environment. Would love the explanation with some nice examples.
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13 Nov 2010, 07:29
Thanks guys...found what i was looking for...you are wonderful..

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16 Nov 2010, 05:52
Bunuel wrote: PERCENTSThis post is a part of [ GMAT MATH BOOK] created by: Bunueledited by: bb, walker This topic is included in GMAT ToolKit App (iPhone/iPod Touch) [ read more] [ AppStore]  DefinitionA percentage is a way of expressing a number as a fraction of 100 ( per cent meaning "per hundred"). It is often denoted using the percent sign, "%", or the abbreviation "pct". Since a percent is an amount per 100, percents can be represented as fractions with a denominator of 100. For example, 25% means 25 per 100, 25/100 and 350% means 350 per 100, 350/100. • A percent can be represented as a decimal. The following relationship characterizes how percents and decimals interact. Percent Form / 100 = Decimal Form For example: What is 2% represented as a decimal? Percent Form / 100 = Decimal Form: 2%/100=0.02 Percent changeGeneral formula for percent increase or decrease, (percent change): \(Percent=\frac{Change}{Original}*100\) Example: A company received $2 million in royalties on the first $10 million in sales and then $8 million in royalties on the next $100 million in sales. By what percent did the ratio of royalties to sales decrease from the first $10 million in sales to the next $100 million in sales? Solution: Percent decrease can be calculated by the formula above: \(Percent=\frac{Change}{Original}*100=\) \(=\frac{\frac{2}{10}\frac{8}{100}}{\frac{2}{10}}*100=60%\), so the royalties decreased by 60%. Simple InterestSimple interest = principal * interest rate * time, where "principal" is the starting amount and "rate" is the interest rate at which the money grows per a given period of time (note: express the rate as a decimal in the formula). Time must be expressed in the same units used for time in the Rate. Example: If $15,000 is invested at 10% simple annual interest, how much interest is earned after 9 months? Solution: $15,000*0.1*9/12 = $1125 Compound Interest\(Balance(final)=\) \(=principal*(1+\frac{interest}{C})^{time*C}\), where C = the number of times compounded annually. If C=1, meaning that interest is compounded once a year, then the formula will be: \(Balance(final)=\) \(principal*(1+interest)^{time}\), where time is number of years. Example: If $20,000 is invested at 12% annual interest, compounded quarterly, what is the balance after 2 year? Solution: \(Balance=20,000*(1+\frac{0.12}{4})^{2*4}=\) \(=20,000*(1.03)^8=25,335.4\) PercentileIf someone's grade is in \(x_{th}\) percentile of the \(n\) grades, this means that \(x%\) of people out of \(n\) has the grades less than this person. Example: Lena’s grade was in the 80th percentile out of 120 grades in her class. In another class of 200 students there were 24 grades higher than Lena’s. If nobody had Lena’s grade, then Lena was what percentile of the two classes combined? Solution:Being in 80th percentile out of 120 grades means Lena outscored \(120*0.8=96\) classmates. In another class she would outscored \(20024=176\) students. So, in combined classes she outscored \(96+176=272\). As there are total of \(120+200=320\) students, so Lena is in \(\frac{272}{320}=0.85=85%\), or in 85th percentile. Official GMAC Books:The Official Guide, 12th Edition: PS #10; PS #17; PS #19; PS #47; PS #55; PS #60; PS #64; PS #78; PS #92; PS #94; PS #109; PS #111; PS #115; PS #124; PS #128; PS #131; PS #151; PS #156; PS #166; PS #187; PS #193; PS #200; PS #202; PS #220; DS #2; DS #7; DS #21; DS #37; DS #48; DS #55; DS #61; DS #63; DS #78; DS #88; DS #92; DS #120; DS #138; DS #142; DS #143; Generated from [ GMAT ToolKit] Attachment: Math_icon_percents.png In the compound interest example, Please let me know how do we calculate 20000*(1.03)^8 . is there any simple way to find (1.03)^8. thanx....

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redwine01 wrote: Hey guys i am new in this forum... can you help me with these percentage problem?
1) The income of a broker remains unchanged though the rate of commission is increased from 4% to 5%. THe percentage slump in business is:
i)1 ii) 8 iii) 20 iv)80
2) p is 6 times as large as q. The percent that q is less than p is:
i) 83.33 ii) 16.5 iii) 90 iv) 60
3) In a market survey 20% voted for A and 60% voted for B. the remaining were uncertain. if the difference between who voted for B and those who were uncertain was 720 how many individuals were covered in the survey?
i) 3600 ii) 1440 iii)1800 iv) cant determine Hi Guys! Can anyone answer to the above questions please? Thank you.

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1)iii 20 Lets say initial income=x, amended income=y then 4x/100=5y/100 ie x/y=5/4 If income declines from 5 to 4, its 20% decrease.
2)i 83.33 p=6q ie p/q=6/1 therefore pq/p=61/6=5/6=83.33%
3)iii 1800 Votes for A=20%, B=60%, uncertain(U)=20% and BU=60%20%=720 ie 40%=720 ie 100%=1800

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Bunuel wrote: gurpreetsingh wrote: Bunuel wrote: PERCENTSExample: Lena’s grade was in the 80th percentile out of 120 grades in her class. In another class of 200 students there were 24 grades higher than Lena’s. If nobody had Lena’s grade, then Lena was what percentile of the two classes combined? Solution:Being in 80th percentile out of 120 grades means Lena outscored \(120*0.8=96\) classmates. In another class she would outscored \(20024=176\) students. So, in combined classes she outscored \(96+176=272\). As there are total of \(120+200=320\) students, so Lena is in \(\frac{272}{320}=0.85=85%\), or in 85th percentile. Attachment: Math_icon_percents.png In another class she would outscored \(20024=176\) students. I think it should be 200241 = 175 as 24 were higher than Lena , thus 24+1 are lower than her, we need to count her as well The point here is that Lena herself is not in the other class. So in another class she outscored 20024=176 not 175. Hope it's clear. But the question does not say Lena is not in other class. So, how to interpret this, based on the provided solutions?
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Bunuel wrote: "Lena’s grade was in the 80th percentile out of 120 grades in HER class. In ANOTHER class ..." So another class is not Lena's class. OK. Thanks. I observed that, but I looked at those two statements "independently", because we are not allowed to make assumptions unless sufficient supporting material is available.
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Bunuel wrote: Chembeti wrote: Bunuel wrote: "Lena’s grade was in the 80th percentile out of 120 grades in HER class. In ANOTHER class ..." So another class is not Lena's class. OK. Thanks. I observed that, but I looked at those two statements "independently", because we are not allowed to make assumptions unless sufficient supporting material is available. It's a PS question, so sentences are not independent like the statements in DS. Check similar GMAT Prep problem: amysgradewas90thpercentileofthe80gradesforher98164.htmlHope it helps. Yes, it helped me lot, Bunnel. I thank you very much. Now, I realized the difference between PS && DS. (shame on me )
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05 Mar 2012, 01:35
Bunuel wrote: gurpreetsingh wrote: Bunuel wrote: PERCENTSExample: Lena’s grade was in the 80th percentile out of 120 grades in her class. In another class of 200 students there were 24 grades higher than Lena’s. If nobody had Lena’s grade, then Lena was what percentile of the two classes combined? Solution:Being in 80th percentile out of 120 grades means Lena outscored \(120*0.8=96\) classmates. In another class she would outscored \(20024=176\) students. So, in combined classes she outscored \(96+176=272\). As there are total of \(120+200=320\) students, so Lena is in \(\frac{272}{320}=0.85=85%\), or in 85th percentile. Attachment: Math_icon_percents.png In another class she would outscored \(20024=176\) students. I think it should be 200241 = 175 as 24 were higher than Lena , thus 24+1 are lower than her, we need to count her as well The point here is that Lena herself is not in the other class. So in another class she outscored 20024=176 not 175. Hope it's clear. This kind of clear thinking is a little aweinspiring, especially when my brain's already turned into oatmeal from 2 months of prepping!
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The formula for percentage is the following and it should be easy to use: Study it below carefully before looking at the examples \(\frac{is}{of}= \frac{%}{100}\) OR \(\frac{part}{whole} = \frac{%}{100}\) We will take examples to illustrate.Let us start with the formula on the left An important thing to remember: Cross multiply It means to multiply the numerator of one fraction by the denominator of the other fraction Examples #1: 25 % of 200 is____ In this problem, of = 200, is = ?, and % = 25 We get: is/200 = 25/100 Since is in an unknown, you can replace it by y to make the problem more familiar y/200 = 25/100 Cross multiply to get y × 100 = 200 × 25 y × 100 = 5000 Divide 5000 by 100 to get y Since 5000/100 = 50, y = 50 So, 25 % of 200 is 50 Examples #2: What number is 2% of 50 ? This is just another way of saying 2% of 50 is___ So, set up the proportion as example #1: is/50 = 2/100 Replace is by y and cross multiply to get: y × 100 = 50 × 2 y × 100 = 100 Since 1 × 100 = 100, y = 1 Therefore, 1 is 2 % of 50 Examples #3: 24% of___ is 36 This time, notice that is = 36, but of is missing After you set up the formula, you get: 36/of = 24/100 Replace of by y and cross multiply to get: 36/y = 24/100 y × 24 = 36 × 100 y × 24 = 3600 Divide 3600 by 24 to get y 3600/24 = 150, y = 150 Therefore, 24 % of 150 is 36 Now, we will take examples to illustrate how to use the formula for percentage on the right Examples #4: To use the other formula that says part and whole, just remember the following: The number after of is always the whole The number after is is always the part If I say 25 % of___ is 60, we know that the whole is missing and part = 60 Your proportion will will like this: 60/whole = 25/100 After cross multiplying, we get: whole × 25 = 60 × 100 whole × 25 = 6000 Divide 6000 by 25 to get whole 6000/25 = 240, so whole = 240 Therefore, 25 % of 240 is 60 Examples #5: ___% of 45 is 9 Here whole = 45 and part = 9, but % is missing We get: 9/45 = %/100 Replacing % by x and cross multiplying gives: 9 × 100 = 45 × x 900 = 45 × x Divide 900 by 45 to get x 900/45 = 20, so x = 20 Here we go!. I hope these formula for percentage were helpful.
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