A shipment of 10 Ford Pintos contains four that will explode if the rear bumper is struck by another car. In how many ways can a used car dealer purchase three of the Pintos and receive: a) three good cars
b) two good cars
c) at least one good car

see explanation

step-by-step explanation:

since the sequence is geometric there is a common ratio r between consecutive terms, that is

r = 4 ÷ - 2 = - 2

r = - 8 ÷ 4 = - 2

r = 16 ÷ 8 = - 2

the next term - 13 must be incorrect as it should be - 32 for the sequence to be geometric.

the first 4 terms are therefore geometric with common ratio r = - 2