# Probability on Defective Tyres

#### rahulranjan86

##### New member
If 3 of 20 tyres are defective and 4 of them are randonly chosen for inspection, what is the probablity that only one of the defective tyres are included?

My Attempt:

= (3C1 * 17C3) / 20C4

= 0.4211

Not sure where I am going wrong. :?:

#### HallsofIvy

##### Elite Member
If the problem is "the probablity that only one of the defective tyres are included" then the book is wrong. I haven't done the calculations but I suspect that the book is giving the probability that "at least one tyre is defective".

#### HallsofIvy

##### Elite Member
Either the book is wrong or the question is NOT "the probablity that only one of the defective tyres are included".

#### pka

##### Elite Member
If 3 of 20 tyres are defective and 4 of them are randonly chosen for inspection, what is the probablity that only one of the defective tyres are included?
My Attempt:
= (3C1 * 17C3) / 20C4
= 0.4211 Book Answer: 0.889
As the question is written, your answer is correct.

Thank You!