Planet 1 Flashcards
Word problems are a good opportunity to…
Backsolve
When a word problem includes variables in the answer choices…
Pick Numbers
Mistakes tend to happen on word problems when…
You solve for the wrong thing (Liters of petrol in the tank vs liters of petrol used)
In word problems, how to assign and treat variables…
Assign for boy as B, not X. Underline what you’re solving for.
Work =
Rate x Time
Distance =
Rate x Time
Rate =
Work / Time
Rate =
Distance / Time
Rates are…
Additive. If two working together, you can combine them for a combined rate.
Multiple rates and changing conditions?
Reset when conditions change
Convert time to?
Rates. Machine 1 can complete the job in 5 hours — 1/5. Remember, a rate is always the inverse of the time for one unit of work.
Collision problems (two people/cars/etc meeting)
Combine their rates
Catching up problems
Subtract their rates
Rate and time are…
Inversely proportional
When given a formula as an answer…
Try number picking
When to use venn diagram?
When you see “both” or “neither” in a word problem, suggesting you are working with overlapping sets
Write out a venn diagram and both equations
A + B - Both + Neither = Total; A only + B only + Both + Neither = Total
When to use matrix boxes?
When you have sets of complimentary information - red vs not red, sold vs not sold
Matrix beware…
When entering percent or fraction information that you are taking it of the right item
Triple venn formula
A + B + C - AB Only - BC Only - AC Only - 2xall 3 + Neither = Total
When matrix boxes provide percent or fraction data, its a good idea to…
Pick your own numbers
Two equations, two variables?
Enough to solve in DS
Remember, if a statement does not say “ONLY” in an overlapping problem…
It does not mean only
Min/Max problems…3 questions…
1) Numbers have to be positive? 2) Numbers repeat? 3) Numbers have to be integers?
To maximize one value…
Minimize the others
To minimize one value…
Maximize the others
Distributing values as close to the average as possible…
Good way to maximize the lower value or minimize the higher value.
Min/max techniques…
Trial and error is important. Generally tough to solve thru algebra
Key words to know you’re dealing with min/max
Greatest # received, least # received, etc.
Don’t assume…
Any rules that aren’t explicitly given
Integers…
Can be negative
Sum of evenly spaced sets principle…
Sum = # of values x med/mean value
Mean in any evenly spaced set is…
(1st term + last term / 2)
You cannot average…
An average. If combining two averages that have been taken from two number sets, you can’t simply average them
Setting up Weight Avg. Equations…
2 setups…Tracking the Mixture equation (0.2X + 0.4Y = .25(12) and tracking the total equation (X + Y = 12)
How to spot when to set up 2 equations on weighted averages?
Asked to average avg’s or percents. Set up as a system of equations algebraically.
Weighted averages lend themselves well to…
Finding ratios and percents
Mapping Strategy…
Can be used for WA problems, specifically for finding ratios
Mixture problems are…
Weighted average problems
When asked about solutions…
Treat as weighted average
Mapping Strategy…
Can flip around and use in different orders
DS in WA problems
Mapping strategy often will give you a ratio, which is all you often need, don’t think you need to solve for every value and variable in the problem for a solution.
Mapping Strategy flaws…
Sometimes it just may not work. Sometimes you will just have to do the algebra
On the GMAT, you are often…
Given easy outs. Think like the test maker. They are not going to make insane questions with insane labor - time is factored into their creation
