## Monday, March 28, 2016

In statistics, if a problem asks for the sensitivity, specificity or accuracy or a test, you just need the following formulas:

Sensitivity = (true positives)/(true pos. + false neg)
Specificity = (true negatives)/(true neg. + false pos)
Accuracy = (true negative + true positive)/total

These values are generally easy to find given a 2 x 2 matrix with the data for the problem

## Tuesday, March 15, 2016

The weights of professional baseball players follow a normal distribution
with a mean of 200 pounds and a standard deviation of 25 pounds.
Find the probability that a randomly selected professional baseball
player has a weight less than 225 pounds, P(x < 225) - ?

Z value is (x-mean)/standard deviation
x = 225
mean= 200
standard deviation = 25
Z = (225 - 200)/25 = 1
Now look up Z(1) on the chart and you will see it is .8413. That is the answer since they are asking for P(x < 225) if it was P(x > 225) then would have to take 1- .8413

## Tuesday, March 8, 2016

Here's an example of solving equations using trig functions.

2sin*sin2x - cosx =0

(know that sin2x = 2sinxcosx, therefore we have

4sin^xcosx - cosx =0

cosx(4sin^2(x) - 1) = 0

cosx = 1,  4sin^2(x) = 1

x = 0,       sin^2(x) = 1/4, sinx = +/- sqrt(2)/2

x= pi/4, 3pi/4, 5pi/4 and 7pi/4