of the 20 members of a kitchen crew , 17 can use the meat - cutting machine , 18 can use the bread - slicing machine , and 15 can use both machines . if one member is chosen at random , what is the probability that the member chosen will be someone who can not use either machine ?
you know how to solve for total number of people who can use at least one machine : total = n ( a ) + n ( b ) - n ( a and b ) total people who can use at least one machine = 17 + 18 - 15 = 20 so all 20 people know how to use at least one machine . hence , if you pick anyone , the probability is 0 that he would n ' t know how to use any machine . answer a
divide(add(subtract(17, 15), subtract(18, 15)), 20)