Cheatography

# SAT Math Techniques ch10 Cheat Sheet (DRAFT) by taotao

This is a draft cheat sheet. It is a work in progress and is not finished yet.

### Plugging In Your Own Numbers (PIYON)

 Whenever you see a problem with variables in the answer choices, Plug In. in terms of; equivalent form messy/­nasty algebra =>s­imple clear arithmetic Try 1, verify with 0 or 2; be careful the number must be in the domain if answers are percents or fractional parts of some unknown quantity try Plugging In: percent = 100*di­ff/­ori­ginal eg total number of marbles in a jar, total miles to travel in a trip ratio percent =>p­lugin ==>­number, 10% =>10

### PLUGGING IN THE ANSWERS (PITA): answer is a number

 If the average (arith­metic mean) of 8 and x is equal to the average of 5, 9, and x, what is the value of x ? Don’t try to solve problems like this by writing equations and solving for x or y. Plugging In the Answers lets you use arithmetic instead of algebra, so you’re less likely to make errors. Start from either end(gr­eatest or least) or middle­(mean) if answer has very small/big number, try bigger­/sm­aller first

### DATA ANALYSIS

 The Average Pie [total­,avg,n] When calcul­ating averages, always find the total. It’s the one piece of inform­ation that ETS loves to withhold. Median To find the median of a set containing an even number of items, take the average of the two middle numbers after putting the numbers in order. Mode the number that appears the most. (Remember: Mode sounds like most.) Range highes­t-l­owest Rate pie =average car speed, work done, average pie Percent transl­atiom percent: /100; of: x; what x; is are equals: = 5 is what percent of 80? 5=x*80/100 what percent of 5 is 80? x*5/100=80 PERCENTS increase and decrease 100* difference / original amt Growth and decay final amount = original amount (1 ± rate)number of changes population growth, radioa­ctive decay, and credit payments RATIOS AND PROPOR­TIONS fracti­on=­par­t/w­hole; ratio=­par­t/part, part+p­art=100 sometimes : fracti­on/­ratio => decimal ratio box [p,p,w­]*[­r,m,a]: fill in known ->calc unknown direct propor­tio­n/v­ari­ation x1/y1=­x2/y2 inverse propor­tio­n/v­ari­ation x1y1=x2y2