A package contains 340 sparking plugs. Eighty of them are single sparking plugs

Question

A package contains 340 sparking plugs. Eighty of them are single sparking plugs and the remaining 260 are double sparking plugs. Two sparking plugs are selected without replacement at random:

a) What is the probability that the first selected is a double sparking plug?

b) What is the probability that the second is double sparking plug, given that the first selected is single sparking plug?

c) What is the probability that the second is double is sparking plug, given that the first selected is also double sparking plug?

Explanation / Answer

(a)

Required probability is:260/340=13/17

(b)

Number of sparking plugs left are: 339 and 260 are double sparking plugs

So required probability is: 260/339

(c)

Number of sparking plugs left are:339 and 259 are double sparking plugs.
So required probability is: 259/339

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