happy1992 wrote:

Thirty airmail and 40 ordinary envelops are the only envelop in a bag. Thirty-five envelops in the bag are unstamped, and 5/7 of the unstamped envelops are airmail. What is the probability that an envelope picked randomly from the bag is an unstamped airmail envelope?

(A) 1/7

(B) 1/3

(C) 13/35

(D) 17/38

(E) 23/70

Here we have 30 airmail and 40 ordinary envelops. Hence a total of 70 envelops.

Now 35 envelops are un-stamped a 25 of them are airmail. Hence the new distribution is :

1. Unstamped airmail 25

2. Stamped airmail 5

3. Unstamped normal envelop 10

4. Stamped normal envelop 30

Hence probability of unstamped airmail envelope should be 25/70.

_________________

Sandy

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