Brainiacs (Part One)

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1. Just checking:
Five kids sit down to play some games of checkers. If each one of the five kids plays one game with each of the others, what is the total number of games played?

2. The one and only:
Believe it or not there is only one number whose letters are in alphabetical order. Can you find it?

3. A very good year:
The year 1978 has an unusual property. When you add 19 to 78, you get 97, the middle two digits of the year! What will be the next year to have the same property?

4. Long division:
Professor Mathman went to the black board and demonstrated to his astonished class that one half of eight is equal to three! What did the professor do?

Remember: Sometimes titles of the riddles contain a hint.

5.  When in Rome:
Were the previous problems too easy? If so, then come up with a way of proving that one half of nine equals four.

6. Two workers are better than one:
If one worker can complete a job in 6 days and a second worker takes 12 days to complete the same job, how long will it take them working together?

7. Three’s a charm:
There is an inexpensive item that can be purchased for less than a US dollar. You could buy it with four standard US dollar coins. If you wanted to buy two of these items, you’d need at least six coins. However, if you bought three, you only need two coins. How much does the item cost?
Recall that you have only five US coins to work your calculations with: a penny (one cent) a nickel (five cents) a dime (ten cents) a quarter (twenty five cents) a half dollar (fifty cents)

It looks hard but is easy peasy..