This site is 100% ad supported. Please add an exception to adblock for this site.

GRE arithmetic

Terms

undefined, object
copy deck

using the average to find the missing number:

ave of 4 numbers is 7. if 3 of the numbers are 3,5, and 8, what is the 4th number? 

To find the missing number when there is an average, use the sum:

  • sum=(ave)x(# of terms)
  • sum=4x7=28
  • add the known numbers, subtract from sum, giving you the 4th number
  • 3+5+8=16
  • 28-16=12 (the 4th number)
    <
average
ave=(sum of terms)/(# of terms)
average of consective numbers

ave of evenly spaced numbers:

  • ave the smallest and largest
  • (a+z)/2
the ave of all a thru z is the same as the ave of a and z.
average rate

ave A per B=(total A)/(totaol B)

ave speed= (total dist)/(total time) 

comparing fractions
  • reexpress fractions with a common denominator
  • or convert both to decimals


3/4=21/28 and 5/7=20/28 (21/28 is greater)

3/4=0.75 and 5/7=0.714 (0.75 is greater) 

converting eighths
1/8= 0.125= 12 1/2%
converting fifths
1/5 = 0.2 = 20%
converting fourths
1/4 = 0.25 = 25%
converting fractions to decimals
divide the bottom into the top
converting tenths
1/10 = 0.1 = 10%
converting thirds
1/3 = 0.333... =33 1/3%
counting consecutive integers

to count consectutive integers:

  • subtract the smallest from the largest
  • add 1

31-13=18

18+1=19 

distance, rate, time
distance= rate x time
dividing fractions
invert the second one and multiply
factors

Factors: + integers that ÷ into n w/no remainder

Multiples: integers that n ÷ into w/ no remainder 

Greatest common factor (GCF)
  • break down numbers into their prime factorizations 
  • take all the prime factors they have in common
  • multiply together for GCF

36=2x2x3x3

48=2x2x2x2x3

GCF=2x2x3=12 

integer
  • a multiple of 1
  • include negetive whole #'s
  • includes 0
Least Common Multiple (LCM)

the smallest number that can be divided into a number:

LCM of 12 and 15?

60 (12 and 15 can both divide into it) 

median
  • the middle value
  •  if there is an even # of values, the median is halfway b/t the 2 middle values
multiples of 2 and 4

an integer is:

  • divisible by 2 if the last digit is even
  • divisible by 4 if the last 2 digits make a multiple of 4 
multiples of 3 and 9

divisible by 3

  • sum of digits is divisible by 3

divisible by 9

  • sum of is digits is divisible by 9 
multiplying fractions
mult. numerators and multiply the denominators
percent

Percent: a fraction w/an implied denominator of 100.

32% = 32/100 = 8/25 

percent increase

To increase a number by a percent:

  • add the percent to 100%
  • convert to a decimal
  • multiply by the number 

25%>40?

  • 25%+100%=125%
  • 125%=1.25
  • 1.25 x 40=50 
Prime numbers

Positive integer that is divisible only by 1 and itself.

Smallest and only even prime # is 2 

probability
probability= (# of desired outcomes)/(total # of possible                                          &
reciprocal

reciprocal of a fraction:

  • switch the numerator and the denominator
  • the product of reciprocals is 1 
remainder

487 is 2 more than 485, which is a multiple of 5.

when 487 is divided by 5, the remainder is 2 

using a ratio to find a number

If the parts add up to the whole, a part-to-part ratio can be turned into 2 part-to-whole ratios by putting easch number in the original ratio over the sum of the numbers.

1:2 men:women in a group of 18 people. how many women are there?

using the ave to find the sum

sum=(ave)x(#of terms)

 

Deck Info

30

bpullar

permalink