# Formulas/Process

 LCM (Least Common Multiple/Factor) Steps: 1) Determine the prime #s2) Take each prime factor to the highest power it appears.3) Multiply together the results of the primes to their highes power Universal Divisibility Strategy: Simply subtract easy to identify multiples of that # until you recognize a factor or non-factor, or 0. ex. 952 divisible by 7? 952 - 700 = 252 ->252 - 210 = 42 ->42-42 = 0 (thus yes, divisible by 7) Divisibility rule 3: # is divisible by 3 if the sum of the digits is a multiple of 3 Divisibility rule 4: # is divisible by 4 if last two digits together is divisible by 4. Ex: 724 Divisiblity rule 6: # is divisible by 6 if even AND sum of digits divisible by 3 Divisibility rule 9: # is divisible by 9 if sum of digits is a multiple of 9 Divisibility rule 11: # is divisible by 11 if difference b/w sums of alternate digits is divisible by 11 ex: 4,983 divisible by 11? 4+8 = 12 9+3 = 12 12-12 (diff b/w sums) = 0 Thus yes 4,983 is divisible by 11 Prime factors vs. Unique Factors: How many prime factors does 20 have? Prime factors vs. Unique Factors: How many unique factors does 20 have? Figure out factors working from greatest to least (outside -> in pairs) 20, 10, 5, 4, 2, 1 Unique factors = 6 Comparing Fractions: A vs C B vs D AD vs BCBD vs BD Multiply denominators for common denominator, then cross multiply numerators Comparing Fractions - which is greater? 3 vs 11 7 vs 25 best way? Since denominators will be the same, just skip calc & compare numerators after cross multiply. 3x25=75 -------- 7x11=77 75 or 77 greater? 77 so... 11/25 greater What is the distance/rate or Work/Rate formula? D=RT or W=RT What is the "trick" to calculating rate? Rate is the inverse of time (only when talking about a full job). ex. T = 6hrs, R = 1/6th per hour What are the 5 important steps to rates? 1) Always convert time to rates2) Rates are additive3) Once you have the necessary rate, plug in the info to W=RT to solve.4) When conditions change, reset equations & solve with multiple equations (not one)5) Recognize if the rate is the same, then time used is proportional to # of workers. More workers = less time & vice versa. % of = % of = (part/whole) x 100 Ex: 15/30 x 100 = 50% % Change = % Change = (New value - Orig Value)/ Orig Value x 100 Greatest common factor/steps? 1) Factor out the #s into primes2) Pick the prime #s out that they both share (only)3) Multiply those prime #s together (only once for ea. #). What's this definition for..."The smallest non-zero # that is a multiple of two or more #s" LCM (least common multiple) What's this definition for... "The largest # that divides evenly into each of a given set of #s" GCF (Greatest common factor or divisor) AuthorJanineG14 ID81553 Card SetFormulas/Process DescriptionFormulas/Process to Memorize Updated2011-06-17T04:31:14Z Show Answers