yes the answer is D. But what is the reasoning??

Erythrovirus412

The Erythrovirus412, which affects farmed Atlantic salmon, infects human beings by adhering to red blood cells. The virus elevates the body’s white blood cell count, indicating that the body is fighting an infection. Surprisingly, when a group of recently-infected people were tested, the proportio...

Thanks Mitch,

i was following it via the 2nd approach that you have mentioned, but got stuck with the probability of the 2nd , 3rd wrong envelopes.
but i got it now, so thanks.
you rock!!

PS: letters and envelopes

@ GMATguruNY:

Q: 4 letters are to be put into 4 envelopes . what is the probability that out of 4 only one letter goes into the envelope with its correct address.

a)1/24
b)1/8
c)1/3
d)1/4
e)3/8

1. x=4y+4, where is an integer. Now put -1 for y. then x becomes 0. so is 0 divisible by 4. I think it is no. So u cant answer with 1. Similar reasoning occurs for 2. So i felt the answer to be E. But Manhattan guide says the answer to be D. 0 is divisble by 4. infact 0 is divisible by any no. sinc...

GMATguruNY: The solution which you have given earlier mentions selection of the boxes, but the question never asks about selecting any box. it only asks for the prob. that any box contains grape. so we need not to go thru this lengthy process. we can simply calculate the probabilities of having grap...