Jan/Feb ’23 Brain Teasers

NOTE:  Newest BTs in red, Bonuses in blue, comments in green, updates in purple.  For reminders on ways to submit answers, see below.

1.  What was special numerically about the first day of 2023? (Possible multiple answers?)
2.  2023 has two months that have a Friday the 13th (Jan & Oct).  Could a year have two consecutive such months?  Explain.
3.  If the radius of a given circle is doubled, how does that affect a) the circumference and  b) the area  of the new circle?
4.  Find the sum of the first three primes and the first three two-digit composites.
5.  Two positive numbers are reciprocals.  If one is four times the other, what are the numbers?
6. 

6.  Sent along by subscriber Amy Ragsdale.  Found on the back of her cereal box.  🙂

7.  Ralph was going the opposite direction of a ONE-WAY sign as he passed the police station.  Two policeman saw him go by, yet he was not arrested.  Why is that? (Very creative solutions smiled at – perhaps accepted.)

8.  Find the sum of the reciprocals of all the whole number factors of 24.

9.  True or False?  The (infinitely) repeating decimal 0.99999 . . .  is actually equal to 1 .

10.  What is the largest three-digit whole number divisible by both 9 and 7?

11.  Easy BT for February:  Is February the only month with 28 days this year?

12.  Non-Math Trivia:  The actress Cindy Williams, co-star of Laverne & Shirley just died recently.  Can you name the TV show from which Laverne & Shirley was a spin-off?

13. A doctor and a bus driver are both in love with Sarah. The bus driver had to go on a long bus trip that would last a week. Before he left, he gave Sarah seven apples. Why?  (Look for the humor.)

14.  What’s 10% of (20% of (40% of (50% of 1000)))?

15.  Have we done this before?  What is special/unique about the number 8,549,176,320?

BONUS #1.  Look at #5 above.  Replace the word “four” with “seven” and work the new problem.

BONUS #2.  Look at #8 above.  Replace “24” with “60” and work the new problem.

BONUS #3:  See #9 above.  Find a proper fraction that is exactly equivalent to the (infinitely) repeating decimal  0.989898 . . .

BONUS #4:  See #1 above.  Going to the opposite end of the year, what will be special numerically about the last day of 2023?

Brain Teaser solutions may be submitted in several ways:  1) Respond directly to the Mailing e-mail.  2)  Use this Contact form.  3)  Use the Comment section below (working to be re-instated, if not already.)