GMAT 01 - Fractions & Decimals Flashcards
3/8 + 1/2 = ?
LCD = 8
= 7/8
3 + 1/4 = ?
3 + 1/4 = 3 1/4
= 13/4
Fractions within the Denominator trick
Fractions that contain a fraction in the denominator can be simplified by putting the numerator over one and multiplying the numerator by the “flip” of the denominator
example:
2/(1/3)
= (2/1) / (1/3)
= (2/1) x (3/1)
= 6
5/7 - 1/3 = ?
LCD = 21
= 8/21
Simplify the Fraction:
75/300
= 1/4
( 75/300 = (3x25) / (3x100) = 25/100 )
( 25/100 = (1x25) / (4x25) = 1/4 )
This fraction breaks down twice
How do you convert a fraction into a mixed numeral?
1) Divide the numerator by the denominator. The number of times that the denominator can go into the numerator determines the whole number portion of the mixed numeral
2) Place the remainder over the denominator. The resulting fraction is the fractional portion of the mixed numeral.
5/7 - 2/7 = ?
= 3/7
(y/4) / (y/x) = ?
= x/4
(y/4) / (y/x) = (y/4) x (x/y)
(y’s eliminate)
= (1/4) x (x/1)
= x/4
(2a/3b) / 2ac = ?
= 1/3bc
(2a/3b) / 2ac
= (2a/3b) / (2ac/1)
= (2a/3b) x (1/2ac)
= 2a/6abc
= 1/3bc
3 3/4 x 7 1/3 = ?
= 55/2
3 3/4 x 7 1/3
= (12/4)+(3/4) x (21/3)+(1/3)
= 15/4 x 22/3
(common denominator = 4x3 = 12)
6 / (4x-x) = ?
= 2/x
6 / (4x-x)
= (2)(3) / (3x)
= 2/x
X - 1/4 = ?
LCD = 4
= (4x-1)/4
1/5 + 2/5 =
= 3/5
(ab2c)/(abc) x (ac)/(abc) = ?
= 1
(ab2c)/(abc) x (ac)/(abc)
= b(abc)/(abc) x (ac)/(abc)
= (b)/1 x (ac)/abc)
= abc/abc
= 1
4 - 1/5 = ?
LCD = 5
= 19/5
14/9 x 6/21 = ?
= 4/9
14/9 x 6/21 = (2x7)/(3x3) x (3x2)/(3x7)
7s and one set of 3s cancel
= (2/3) x (2/3)
= 4/9
6 + 2/x = ?
6 + 2/x = 6 2/x = (6x + 2) / x
Simplify the Fraction:
14/98
= 1/7
( 14/98 = (2x7) / (2x49) = 7/49 )
( 7/49 = (1x7) / (7x7) = 1/7 )
This fraction breaks down twice
7 1/4 - 4 1/2 = ?
= 11/4
7 1/4 - 4 1/2
= (28/4)+(1/4) - (8/2)+(1/2)
= 29/4 - 9/2
(common denominator = 4)
29/4 - (2/2)(9/2)
= 29/4 - 18/4
= 11/4
Fractions within the Numerator Trick
Fractions that contain a fraction in the numerator can be simplified by putting the denominator over one and multiplying the numerator by the “flip” of the denominator
Example:
(2/3)/4
= (2/3) / (4/1)
= (2/3) x (1/4)
= 2/12
= 1/6
Convert into a Mixed Fraction:
38/7
= 5 3/7
( 38/7 = 5 remainder 3)
Convert into a Mixed Fraction:
25/4
= 6 1/4
(25/4 = 6 remainder 1)
(11-1) / (2+3) = ?
= 2
(11-1) / (2+3)
= 10/5
= 2
How do you add fractions with different denominators?
To add fractions with different denominators
1) first you must ffind the lowest common denominator (LCD)
2) then you must convert each fraction to be added into a new fraction by multiplying the numerator and the denominator of each fraction by the value that raises each denominator to the LCD.
This process is known as converting fractions to equivalent fractions
Simplify the Fraction:
24x4y3/18x2y2
= 4x2y/3
( 24x4y3/18x2y2 = {(4x2y)(6x2y2)} / (3)(6x2y2) = 4x2y/3 )
The 6x2y2s cancel out
If the numerator of a fraction is zero
The value of the fraction is zero
(1+2) / 6 = ?
= 1/2
(1+2) / 6
= 3/6
= 1/2
How do you simplify a fraction that contains a fraction within its numerator and/or denominator?
To simplify a fraction that contains a fraction within its numerator and/or denominator, always multiply the numerator by the “flip” of the denominator.
example =
(2/5) / (1/3)
= (2/5) x (3/1)
= 6/5
How do you subtract whole numbers and fractions from one another?
To subtract whole numbers and fractions from one another:
a) place the whole number over 1
b) find the LCD between the whole number and the fraction
c) convert the numbers to a shared denominator
d) subtract one number from the other
X + 4/5 = ?
X + 4/5 = X 4/5 = (5x + 4)/5
Definition: Reciprocals
Reciprocals are any two numbers whose product equals 1.
>> While commonly thought of as “flips” that there are also reciprocals that assume different forms – in particular, look to reciprocals involving roots <<
It is also important to remember that a fraction may have more than one reciprocal
>> To determine whether two numbers are reciprocals, always multiply them together <<
Simplify the Fraction:
700/28
= 25
( 700/28 = (7x100) / (7x4) = 100/4 )
( 100/4 = (25x4) / (4x1) = 25)
This fraction factors twice
12/(2/5) = ?
= 30
12/(2/5)
= (12/1) x (5/2)
= 60/2
= 30
(Y/4) x (Y/X) = ?
= Y2/4X
(Y/4) x (Y/X) = (YxY) x (4X)
= Y2/4X
Rule: Working with Mixed Numerals
When working with mixed numerals, always convert the mixed numerals into fractions before adding, subtracting, multiplying, or dividing.
How to express a whole number as a fraction
Set the whole number as a fraction over 1
What is the reciprocal of k + (g/x), where k+(g/x) does not = 0?
= x/(kx+g)
k + (g/x)
= (k/1)(x/x) + (g/x)
= (kx + g)/x
Reciprocal = x/(kx + g)
5 + 2/3 = ?
5 + 2/3 = 5 2/3
= 17/3
(173 + 172) / (172) = ?
= 18
<< Complex Numerator Shortcut>>
(173 + 172) / (172)
= (173/172) + (172/172)
= (17/1) + 1
= 18
15/100 x 45 = ?
= 27/4
15/100 x 45 = (5x3)/(4x5x5) x (3x3x5)/1
= 3/4 x (3x3)
= 27/4
(282 + 28) / 28 = ?
= 29
<< Complex Numerator Shortcut>>
(282 + 28) / 28
= (282/28) + (28/28)
= (28/1) + 1
= 29
In which of the following pairs are the two numbers reciprocals?
a) 2/5 and 5/2
b) (root 5/2) and (2 root 5/5)
c) (root 5/2) and (2/root 5)
= a, b, and c
all options = 1
(2 3/4) / (5 1/2) = ?
= 1/2
(2 3/4) / (5 1/2)
= (8/4)+(3/4) / (10/2)+(1/2)
= (11/4) / (11/2)
= (11/4) x (2/11)
(eliminate 11s)
= 2/4
= 1/2
(4x-x) / (2x+7x) = ?
= 1/3
(4x-x) / (2x+7x)
= 3x/9x
= (3/3) (x/3x)
= 1/3
The Complex Numerator Shortcut
In complex fractions, if the numerator of a fraction contains addition or subtraction, that fraction can be split to simplify the arithmetic.
example:
(282 + 28) / 28 = (282/28) + (28/28)
= 28/1 + 1
= 29
This CANNOT be done with a complex denominator!
(a/b) / (c/d) = ?
= (ad)/(bc)
(a/b) / (c/d)
= (a/b) x (d/c)
= (ad)/(bc)
(5/80) / (2/24) = ?
= 3/4
(5/80) / (2/24)
= (5/5)(1/16) / (2/2)(1/12)
= (1/16) / (1/12)
= (1/16) x (12/1)
= 12/16
= (4/4)(3/4)
= 3/4