by chusbaez Wed Jul 14, 2010 10:54 pm
If you understand why the events must be mutually exclusive then you could never be wrong, because when you design the matrix, each column and row will amount to a sensible TOTAL.
example,
15% of all the guys at work sat for the GMAT, while 80% of the girls did not sit for the GMAT.
there are 200 people at work, 50% are guys.
......SAT GMAT......DID NOT.....TOTAL
GUYS ......15 ............. 85 ..........100
GIRLS ......20............. 80 .......... 100
TOTAL ......35............165 ........... 200
that is, TOTAL GUYS: 100, TOTAL GIRLS:100
TOTAL people who sat GMAT: 35, TOTAL who did not: 165
try to put "guys" next to "SAT GMAT" in a row, does it make sense?