Riddle:
The title of the problem tells you how to approach these four questions.
(A). A bus leaves Moscow for Tula at noon. An hour later a cyclist leaves Tula for mosco, moving slower than the bus. When the bus and cyclist meet, which one of the two will be farther from Moscow?
(B). Which is worth more: a pound of $10 gold peices or half a pound of $20 gold pieces?
(C). At six o'clock the wall clock struck 6 times. Checking with my watch, I noticed the time between the first and last strokes was 30 seconds. How long will the clock take to strike 12 at midnight?
(D). Three swallows fly outward from a point. When will they all be on the same plane in space?
Now check the answers. Did you fall into any of the traps which lurk in these simple problems?
Answer: (A). Neither
(B). A pound of metal is always more than half a pound of the same metal.
(C). Six strokes took 30 seconds, therefore 12 strokes will take 60 seconds. But when the clock struck six, there were only 5 intervals between strokes, and each interval was 30/5=6 seconds. Between the first and twelfth strokes there will be 11 intervals of 6 seconds each, therefore 12 strokes will take 66 seconds.
(D). There is always a plane that contains any 3 points
Riddle:
Two cyclists began a training run, one starting from Moscow and the other starting from Simferopol.
When the riders were 180 miles apart, a fly took an interest. Starting on one cyclists shoulder, the fly flew ahead to meet the other cyclist. After reaching him the fly then turned around and yet back.
The restless fly continued to shuttleback and fourth until the pair met; then settled on the nose of one rider.
The flys speed was 30 mph. Each cyclist speed was 15 mph.
How many miles did the fly travel?
Answer: The cyclists took 6 hours to meet. The fly traveled 6*30=180 miles.
Riddle:
When was the latest year that is the same upside down?
Answer: 1961.
Riddle:
A man phoned his daughter to ask her to buy a few things he needed for a trip. He told her she would find enough dollar bills for the purchase in an envolope on his desk. She found the note with 98 written on it.
In the store she bought $90 dollars worth of things, but when it was time to pay she not only did have $8 left over but she was short.
By how much and why?
Answer: (A). $4. She had read 86 upside down.
(B). Turn 9 upside down and exchange it with the 8. Both columms will add to 18.
Riddle:
When my father was 31 I was 8. Now he is twice as old as me. How old am I?
Answer: The difference in age is 23 years, so I must be 23 if my father is twice as old as me.
Riddle:
A boy has as many sisters as brothers, but each sister has only half as many sisters as brothers.
How many brothers and sisters are there in the family?
Answer: Four brothers and three sisters.
Riddle:
Can you combine plus signs and five 2's to get 28? Can you combine plus signs and eight 8's to get 1,000?
Answer: 22+2+2+2=28; 888+88+8+8+8=1,000
Riddle:
Using only brackets, parentheses, and these signs +,-, X, /. How can you express 100 with 5 1's and express 100 three ways with five 5's?
Answer: 111-11=100
(5 x 5 x 5)-(5 x 5)=100; (5+5+5+5)x 5=100;(5 x 5)(5-(5/5)=100.
Riddle:
What are three ways you can add 4 odd numbers and get ten?
Answer: 1+1+3+5=10
1+1+1+7=10
1+3+3+3=10
Riddle:
Given two 2s, "plus" can be changed to "times" without changing the results: 2 + 2= 2 x 2.
The solution with three numbers is easy too: 1 + 2 + 3= 1 x 2 x 3.
What is the answer for 4 numbers and for 5 numbers?
Answer: Solution for 4 numbers:
1 + 1 + 2 + 4= 1 x 1 x 2 x 4.
Solution for 5 numbers:
1 + 1 + 1 + 2 + 5= 1 x 1 x 1 x 2 x 4
1 + 1 + 1 + 3 + 3= 1 x 1 x 1 x 2 x 4
1 + 1 +2 + 2 + 2= 1 x 1 x 2 x 2 x 2
