Solution:

45

1/5 of 45 = 9
9 + 45 = 54

Solution:

I'm a jigsaw puzzle piece.

Solution:

Firstly: Policeman should take the thug across the river thames and escort the boat back with him. (Thug across, everyone else on this side)
Then, Policeman will take one cat along, leave it there, and on the way back, bring back the thug (since thug cannot be left with anyone without policeman's supervision).
Then Mrs. Mother will take the second cat on the other side. Drop it there and bring the boat back. For the 4th trip, Mrs. Mother And Mr. Father Will travel to the other side, and Mrs. Mother will stay there, and MR. Father will bring the boat back. (Now Mrs. Mother and 2 cats are on the other side.)
5th trip, the policeman takes the thug across. Both of them stay there and Mrs. Mother will come back. Then for the next trip, Mr. Father and Mrs. Mother will go on the boat, and Mrs. Mother will stay there, and Mr. Father will return back.
Then for the 7th trip, Mr. Father will travel with one dog. On the return, the policeman and the thug will return. Then in the next trip, the Policeman will take the second dog. (Now Mrs. Mother and her two cats; Mr. Father and his two dogs and the Policeman is here).
Now finally the policeman takes the boat on the other side and brings back the thug.
Tough one, right ?

Solution:

9 x 8 - 7 + 6 x 5 - 4 = 91.

Solution:

There is a chance of 1/3 to be its best in all the shots. The reason for this is that the shots do not depend on the shot that is made earlier. The chance for the third shot to be its best is 1 minus the chance that the last shot is the best shot. Therefore the answer for this question is 2/3.
There are also other possibilities. There are three arrows A, B, and C. the B arrow is away from the arrow A. so after the shot A the following will be the outcome or the possibility with the shots.
Best shots: A, A, C
Worst shots: C, B, B
From all the three outcomes, the arrow C is worse than the arrow A.

Solution:

7 Races.

Solution:

Solution well explained in picture below.

Solution:

The series are prime numbers with one added to it.
The original prime numbers are as follows.
101, 103, 107, 109, 113, 127

Solution:

If two widows, each having a son married the son of the other widow, and then by the consummation of marriage, both the couples had a daughter, all the aforementioned relationships will turn to be true.

Solution:

{a +b +abs (a-b)}/2
It is shown that {a +b-abs (a-b)}/2 is < {a, b}