If we look carefully on the facts we can see that:
when we take different flavors the number of strawberries remains the same (we took one and put one back) and the  number of blueberries decreases.
However when we take the same flavor, the number of blueberries will decrease by one (if we took 2 blueberries) or increase by one (if we took 2 strawberries), but the number of strawberries can not be decreased by one. So because the  number of strawberries is even means that no matter how many blueberries we have we will get a positions that we are left with two strawberries, and when we take them both we end at a situation where all that’s left is only blueberries. So the  flavor left will be blueberry.

Saying  that “Each lord paid 9 pounds (10 originally and got one back)” is wrong!! They paid 25 pounds and each of them got 1 pound so 25+3 =28 pounds + 2 pounds to the porter is 30.
(Or if you go backwards they paid 30 pound and 2 pounds took the porter and each of the one pound so they paid 25 in total).

You can also look at this riddle as if the paid 25 pounds and gave 2 pounds as a tip to the porter and got 3 pound back.

Aswer: 19
explanation: This sequence is a combination of two series of number: The 1st is: 30, 15, 0, -15 (going down by 15) and the 2nd: 10, 13, 16, 19 (going up by 3)

Saying  that “Each lord paid 9 pounds (10 originally and got one back)” is wrong!! They paid 25 pounds and each of them got 1 pound so 25+3 =28 pounds + 2 pounds to the porter is 30.
(Or if you go backwards they paid 30 pound and 2 pounds took the porter and each of the one pound so they paid 25 in total).

You can also look at this riddle as if the paid 25 pounds and gave 2 pounds as a tip to the porter and got 3 pound back.

9 – 8 + 7 + 65 – 4 + 32 – 1 = 100

If we say that the radius of the big wheel is R than the radius of the small wheel will be 1/3R. The Perimeter of the circle that the small wheel does is 2*pi*(R+1/3R)=2*pi*4/3R. The perimeter of the small wheel is 2*pi*1/3R so if we divide the them we get 4 turns.

Answer:
The moves are:
1) turn two coins if opposite corners
2) two random coins placed next to each
3) same as 1
4) turn any coin
5) same as 1
6) same as 2
7) same as 1
8) flip all coins
9-15) same as 1-7

Explanation: moves 1-7 will cause the coins to be all head or all tails (where 7 is the worst case),  but if after the 7th step the game is not over yet that means we started the game with all coins as tails or we got an all tails
situation during the steps. so that’s why on the 8th step we flip all the coins and repeat the process. (The worst case is indeed when we  start with all coins as tails!!)

Notice that the moves 1,2,3,5,6,7 doesn’t change the number of pair of coins already is head position. move 4 does.
Now if at beginning we had 2 heads than if thy were diagonal than after step on we get all heads or all tails. If they are next to each other than step 2 will cause them to became diagonal and step 3 will bring us to the same result as step 1.
But this will not work is the initial state was even number of heads/tails. So that’s why on step 4 we turn only 1 coin. So now we are sure that we have 2 tails and 2 heads so we repeat steps 1-3.
In all those cases (2,2 or 1,3) the worst case will be that only on the 7th step we get all tails or all heads and so step 8 will stop the game if we got the all tails situation.
But if we started with all the coins as tails we will need 7 more steps.

There is no solution!! Because Tracy leaves on the 3rd floor and since Sia gets out after Tracy and before Peter means she must be located on the 4th floor and above and peter must be located on the 5th or 6th floor. But since Simon stays in the elevator for the longest time it means he is on the 6th floor and therefor Sia is on the 4th and Peter on the 5th. That means that there is no way that Debra can leave after Tracy!!

Although the answer above is a good one but there is another option: if 1+9+8 = 1 than you might say that 9+8=0 and so 2+9+8 will be 2!!