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### What is the equation for combinations

order DOESN'T matter (without repetition, like lottery)

C = n! / ((n-k)k!)!

where k = number of objects selected from a pile of n objects

n = total number of objects from which k objects can be selected

### what is the equation for permutations

order DOES matter

P = n^r (WITH REPETITION, r is how many you choose, n is total number of choices)

P = n! / (n-r)! (withOUT REPETITION)

where r = number of objects selected from a pile of n objects

n = total number of objects from which r objects can be selected

*if you are selecting all of them the formula is just n!

### What is the quadratic equation

used to find the roots of polynomial equation of the second degree

x = (-b (+-) SQROOT(B^2 - 4AC)) / 2a

### What does P(E) mean

P(E) = number of outcomes in E / total number of possible outcomes.

EX. P({1,3,5}) and total set is {1,2,3,4,5,6}, => P({1,3,5}) = 3/6

### What does it mean to say that two sets are mutually exclusive events

if the event "E and F" is impossible. P(E and F) = 0

### What does it mean tot say that sets A and B are Independent?

Two events A and B are said to be Independent if the occurrence of either even does not alter the probability that the other event occurs

P(A and B) = P(A)P(B)

### What is a polygon

closed plane figure formed by three or more line segments (sides) each side intersects exactly two other sides at their endpoints.

### if machine X can produce 1,000 bolts in 4 hours and machine Y can produce 1,000 bolts in 5 hours, in how many hours can machines X and Y, working together at these constant rates, produce 1,000 bolts?

solve for (1/4) + (1/5) = (1/h)

### If A and B and do a job in 4 hours when working together at their respective constant rates and A can do the job alone in 6 hours, in how many hours can B do the job alone

solve for (1/6) + (1/B) = (1/4)