Prep - Gmat all the quant: the definitive guide to the quant section of the gmat

CHAPTER 1

In this chapter, you will learn the basicusage of fractions, decimals, and percents, as well as how to move back and forthquickly among the three. Youll also learn what kinds of calculations are most easilyperformed in which form.

CHAPTER 1 FDPs

FDPs stands for fractions, decimals, andpercents. These three forms are grouped together because they are different ways torepresent the same number. For example:

Afraction consists of a numerator and a denominator:
Adecimal uses place values:	0.5
Apercent expresses a relationship between a number and100:	50%

All three are equal to each other andrepresent the same number:

Ratios are closely related to fractions butnot quite the same; youll learn more about ratios in a couple of chapters.

The GMAT often mixes fractions, decimals,and percents in a single problem, and certain kinds of math operations are easier toperform on one form compared to the others. In order to achieve success with FDPproblems, you need to shift amongst the three accurately and quickly. Try thisproblem:

A sum of money is divided among threesisters. The first sister receives of the total, the second receives of the total, and the third receives the remaining $10. How many dollars dothe three sisters split?

1. $10
2. $20
3. $30
4. $40
5. $50

To solve, you have to figure out whatproportion of the money the first two sisters get so that you know what proportion thethird sisters $10 represents. The information is provided in fractions, and its nottoo difficult to add up the relatively simple fractions and However, harder fractions would make the work a lot more cumbersome. Ingeneral, adding fractions is annoying because you have to find a common denominator.

Decimals and fractions are much easier toadd. Because the problem talks about parts of a whole, convert to percentages. The firstsister receives 50% of the money and the second receives 25%, leaving 25% for the thirdsister. That 25% represents $10, so 100% of the money is 4 times as much, or $40. Thecorrect answer is (D).

In order to do this kind of math quickly andeasily, youll need to know how to convert among fractions, decimals, and percents.Luckily, certain common conversions are used repeatedly throughout the GMAT. If youmemorize these conversions, youll get to skip the calculations. The next two sectionsof this chapter cover these topics.

Save yourself time and trouble by memorizingthe following common equivalents:

Fraction	Decimal	Percent
	1	100%
	0.5	50%
	1.5	150%

	0.25	25%
	0.75	75%
	1.25	125%
	1.75	175%

	0.125	12.5%
	0.375	37.5%
	0.625	62.5%
	0.875	87.5%

	0.2	20%
	0.4	40%
	0.6	60%
	0.8	80%

Fraction	Decimal	Percent
	0.1	10%
	0.3	30%
	0.7	70%
	0.9	90%

		33.3%