Solution:

2-3
3-4
7-8
9-10

Solution:

The total number of students is 500.

To follow how and why, please see the venn diagram.

Solution:

17

Explanation:
Let us begin with the small square. Let us assume that their size is 1 inch.

Now, number of 1 inched squares = 12 (make sure that you don't count the 4 squares in middle twice.)
Number of 2 inched squares (double size) = 5.

Therefore, total squares = 12 + 5 = 17.

Solution:

2nd

When the cylinder is spun for the first and last time, the following six outcomes are possible:

First:
First chamber is fired first. The first player loses.

Second:
Second chamber is fired first. The first player loses.

Third:
Third chamber is fired first. The first player loses.

Fourth:
Fourth chamber is fired first. The second player loses. (First shot, player 1, chamber 4 empty. Second shot player 2, chamber 5, empty. Third shot player 1, chamber 6 empty. Fourth shot player 2, chamber 1 not empty.)

Fifth:
Fifth chamber is fired first. The first player loses. (First shot, player 1, chamber 5 empty. Second shot player 2, chamber 6, empty. Third shot player 1, chamber 1 not empty.)

Sixth:
Sixth chamber is fired first. The second player loses. (First shot, player 1, chamber 6 empty. Second shot, player 2, chamber 1, not empty)

Thus, if you analyze, you will find that the second player has a 4/6 chance of winning. Therefore if you want to win the game, going second gives you better shot at it.

Solution:

16 (5 + 1 + 1 + 4 + 5)

black coloured squares : 5
red coloured square : 1
blue coloured square : 1
small green coloured squares in middle : 4
large green coloured squares : 5

Solution:

Up to a point

Solution:

75km

Explanation:
Distance between Bill and Darren = 40 km
Distance between Bill and Chris + Distance between Chris and Darren = 40 km
Distance between Bill and Chris + (Distance between Bill and Chris - 10) = 40 km
2 * Distance between Bill and Chris = 50 km
Distance between Bill and Chris = 25
Distance between Chris and Darren = 15 km

Therefore, distance between Darren's house and Alex's house = 60 + 15 = 75 km.

Solution:

Like there is no tomorrow.

Solution:

The time at first observation:
1:12

The time at second observation:
3:24

Thus, two hours and twelve minutes have passed between the two observations.

Solution:

Ted will choose Ann.

You can know why after replacing each letter with the number corresponding to that letter (A = 1, B = 2, C = 3... etc.)

TED = 20 + 5 + 4 = 29
ANN = 1 + 14 + 14 = 29

If you calculate in a similar manner for George and Mary, you will find that each one of them adds up to 57