[mdrm0829]

:confused: A sample of 100 wood and 100 graphite tennis rackets are taken from the warehouse. If 10 wood and 19 graphite are defective and one racket is randomly selected from the sample, find the probability that the racket is wood or defective.

[galactus]

A good thing to do with these types of problems is to make a chart.

                                      WOOD                       GRAPHITE              TOTAL
--------------------------------------------------------------------------------------------------

DEFECT                            10                               19                      29   

--------------------------------------------------------------------------------------------------
NOT DEFECT                    90                               81                       171

-----------------------------------------------------------------------------------------------------
                                    100                            100                   200

Now, look at the graph. The probability it is wood is clearly 100/200

The probability it is a defect is 29/100

But, we have to subtract off the double count, that it's wood and defective, which is

10/200

So, we have

See?