Solution:

One thing you must take note of is that in the question they are talking about pair of socks not individual socks.

Thus, total socks = (9x2) + (8x2) = 18 + 16 = 34
Total possibilities = 34*33*32/3*2*1 = 5984

The next part can be a little tricky. Read the question again. You are asked to calculate the probability that she will pick up a pair of blue socks. That also includes picking up three blue socks.

Thus our favorable events = select 2 blue + all 3 blue
= (18*17/2*1)(16/1)+ (18*17*16)/(3*2*1)
= 2448 + 816
= 3264

Hence the Probability = 3264/5984 = 6/11 = 0.54545

Solution:

In the first wave, let us make an assumption that there is only 1 red hat and other 8 hats are blue. The student who can see all the other 8 blue hats on others' head will certainly be clear that there are 8 blue hats and 1 red hat since the professor told them that there is at least 1 red hat among the nine. But no one was able to answer after the first half an hour. Thus this can't be possible and our assumption is wrong.

Now let us assume that there are 2 red hats and 7 blue hats. The student who is having a red hat on his head can definitely see 7 blue hats and one red hat. He can deduce that he is wearing a red hat. But nobody was able to answer in the second interval as well. Thus our assumption is again wrong.

In the last wave of final five minutes, let us assume that there are 3 hats and 6 blue hats. The student with a red hat can see 2 other red hats and 6 blue hats and he may deduce that he is wearing a red hat. In this interval, everyone was able to answer which states that our assumption is correct.

Thus there are 3 red hats and 6 blue hats.

Solution:

The human in front will count the number of green hats and if the count is an odd number, he will say green and if the number is even, he will say pink.

The next human behind him definitely saw either an odd or an even number of hats. If the number is still odd, then he has a pink hat. That human says Pink and survives. Thereafter, there will be an odd number of green hats forward and the third person can decide whether he is wearing a green hat or a pink hat.

If the second person sees an even number of green hats, then he must have a green hat as well and will be freed. In this fashion, the humans will just have to keep the track if the number of green hats in front of them are odd or even in number and then they can spontaneously conclude with the color of their hats.

Since the first human will be guessing, he will have a 50/50 chance of surviving but the other 9 people will definitely be saved.

Solution:

There are many ways in which you can think a solution for the problem. Your approach should be to minimize the efforts. What if you took out one candy from the box labeled Peach and Grape?

What you have to consider is the fact that every box is labelled incorrectly. Thus if you pick a candy from the box labelled with Peach and Grape, it is evident that the box will not have a mixture of both (as it is labelled wrong). Thus you will get to know which candies are present in that box.

Suppose the candy you take out turns out to be peach flavored, then the box labeled as Grapes is the one which contains a mixture of both peach and grapes. This is because it is labelled incorrectly and since we have already figured out the box with Peach candies, we can be confident of the fact. And then the jar labelled as peach will be the one containing grape flavored candies.

If the candy you take out from the mixed labeled box is Grape flavored, you can use the same logic to find out the rest.

Consider picking a candy from the other two boxes instead of what is told in the solution and you will find out that you will have to take out a candy from each of the boxes before being sure.

Solution:

Let the age of Camilla = x
Then the age of Bella will be 2x
And the age of Anna will be 2x + 2

Now according to the question
(2x + 2) + 2x + x = 27
5x = 25
x = 5

Thus the age of Camilla is 5 years

Age of Bella = 2x = 2*5 = 10 years.