DAY 431

Give me an X, I'll turn to face you.
Give me a cross, I'll turn my back on you.

OR

Give me a cross, I'll turn to face you.
Give me an X, I'll turn my back on you.

Who am I?

Answer:

The number 9:

9 x 9 = 81
9 + 9 = 18

OR

9 + 9 =18
9 x 9 = 81

DAY 430

Puzzle by Sam Loyd (1841-1911):

Arrange three 9's in any mathematical configuration to total 20.

HINTS:
#1: The solution involves only addition and division.
#2: The solution involves a decimal.

Answer:

9 + 9 
   .9

DAY 429

B = 5
C = 6
N = 7
O = 8
? = ?

What is the next entry in this series?

Answer:

F = 9 (Atomic Numbers of elements from the Periodic Table)

DAY 428

IT ALL ADDS UP
Credit: GAMES Magazine
July, 1985
Michael W. Ecker

You and an opponent alternate picking numbers from 1 to 6, and a running total is kept. If the object of the game is to make the score total exactly 50, and you go first, what number should you pick to force a win for yourself?

Answer:

1 .............. 50 is one more than a multiple of 7. If you pick 1 as your number, then, no matter what your opponent chooses, you say 7 minus that number. On your eighth turn, you will cause the score to hit 50 exactly.

DAY 427

THE RACE TO MECCA

A rich Arab who loved puzzles died. In his will he specified that his two sons race one another on horseback. They were to race to Mecca, 20 miles away.  The son whose horse finished last would inherit all his father's wealth.

The day of the race each brother rode his horse as slowly as he could. When night came, they had only gone one mile. At that rate, the race would last at least three weeks, and what would happen when they reached the finish line? That night they stopped at an inn. When they told the innkeeper about their problem, he thought for a minute. He then gave the brothers two words of advice, which they decided to follow.

Early the next morning, they rode off toward Mecca. But now they raced as fast as their horses would carry them. What were the clever innkeeper's two words of advice?

Answer:

"Switch horses." 

DAY 426

LOOSE CHANGE
Credit: GAMES Magazine
July, 1983
Jerry Weinberg

You probably collect a handful of change (pennies, nickels, dimes, and quarters) every day. Which coin, on average, will you receive the least of - and why?

Answer:

Nickels ............. Suppose that 99 people go into a store, one after another, and purchase items costing 1 cent, 2 cents, 3 cents .......... through 99 cents, giving the storekeeper a $1 bill in each case. Assuming the storekeeper has sufficient pennies, nickels, dimes, and quarters, and distributes them in the standard manner (a dime instead of two nickels, etc.), the change will break down thus: 200 pennies, 40 nickels, 80 dimes, and 150 quarters. 

If you still have doubts, try holding your change aside for a week or two, and see for yourself.

DAY 425

PASS THE SOAP
Credit: GAMES Magazine - Mar. 1983
Clara Hall

The cold-water tap fills our tub in 6 minutes 40 seconds, the hot water tap in 8 minutes. The tub drains in 13 minutes 20 seconds. If the stopper is out and the taps run full force, how long will it take the tub to fill? (And how much water will be wasted?)

Answer:

The tub will fill in 5 minutes........The cold faucet fills the tub in 400 seconds (1/400 per second), the hot faucet in 480 seconds (1/480 per second). The tub empties 1/800 of its contents per second. So with both faucets and the drain working together, 1/400 + 1/480 - 1/800, or 1/300 of the tub, gets filled each second. Therefore, the tub will be filled in 300 seconds, or five minutes. Since 1/800 of a full tub empties each second, the amount of water wasted  is 1/800 of a second X 300 seconds = 3/8 of a full tub.