Answers to last issue's Brain Teasers

1. If a clock takes six seconds to strike six times at six o'clock, how
many seconds will it take to strike eleven times at eleven o'clock?
Another Clock Riddle

Ans: 12 seconds. The timing would naturally start on the first strike.
At six, there would be five more strikes in the next six seconds, for a
time of 1.2 seconds per strike. After the first strike at eleven, the
following ten strikes would then take 12 seconds.

2. On May 5, 2006, three clocks were set at noon. The following day at
noon, one was found to be a minute slow, another a minute fast, and the
third still had the exact time. If they continue at the same speeds, on
what date will they once again all read 12:00?

Ans: One must lose twelve hours and the other gain twelve to read the
same as the correct one. Twelve hours is 720 minutes, so it will take
720 days from the first day to all be sychronized at 12:00 again. This
would be on April 24, 2008 (2008 is a leap year).

3. Matchstick:
Try to rectify a mistake by moving a single matchstick, to get the
correct equation.
(You cannot place any matchstick diagonally over the equals sign)

The following equation is made of 11 matches:
XI - V = IV

The following equation is made of 11 matches:
X + V = IV

The following equation is made of 10 matches:
L + L = L

Ans:

. XI - V = IV: Move the single match in XI to the left to get IX - V = IV 
or move it to the place after V: X - VI = IV .

. X + V = IV: Move the match from the + sign to the place before X to
get IX - V = IV .

. L + L = L: Move the horizontal match in L to the right to get
I + L = LI .

Other solutions are also possible.