All posts by mathconfidence

brain puzzler, brain teaser

August 2019 Brain Puzzler Solution

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Q: On an analog clock, how many times do a clock’s hands overlap in a one week period?

A: 154
At 12:00, the hands exactly overlap but not at other times — for example, at 1:05, the hour hand has moved slightly… and at 6:30, the hour hand is halfway between the 6 and the 7.

Making the times that they will overlap only 11 times in 12 hours (60 minutes /11).

12:00, 1:05ish, 2:10ish, 3:15ish, 4:20ish, 5:25ish, 6:30ish, 7:35ish, 8:40ish, 9:45ish, 10:50ish.
In one day they will overlap 22 times so in one week, 154 times.

brain puzzler, brain teaser

July 2019 Brain Teaser Solution

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A wooden cube that is 20 cm on each side is composed of 1 cm x 1 cm x 1 cm  cubes.
Q1: If you paint all 6 sides of the outside of the cube blue, how many cubes will have no blue paint?
With a 3 by 3 by 3 cube, there is just one cube in the middle that would have no paint.
With a 4 by 4 by 4 cube, there are 8 cubes in the center of the cube (2 x 2 x 2) with no paint.
With a 5 by 5 by 5 cube, there are 27 cubes in the center of the cube (3 x 3 x 3) with no paint.

Answer: The pattern continues so a 20 by 20 by 20 cube, there would be 18 x 18 x 18  (5832) cubes in the center of the cube with no paint.

Q2: What if the 20 x 20 x 20 cm cube is composed of 2 cm x 2 cm x 2 cm cubes?
Answer:  There would now be 1000 cubes (10 x 10 x 10), there would be 8 x 8 x 8 (512) cubes in the center of the cue with no paint.

metacognition, non-calculator, Teaching Philosophy

Why Learn to do Math by Hand?

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            Division Jluy 2019       There’s a connection between pencil, paper and brain.

My chairman who is 20 years my junior has lit upon an old idea: help students understand Math without the crutch of a calculator.  This summer, I will teach arithmetic along with algebraic and geometric skills to rising college freshmen to boost their analytical skills, critical thinking and mathematical breadth.  One of the goals is to help students see how much understanding the times tables contributes to the knowledge and skills for high school and college Math.

After teaching Math for Elementary Educators for over 10 years, I can appreciate how the classroom can differ without the use of technology.    This is like going back home as I am from the last millenium aka BC Before Calculators.

Some of the topics we will cover include multiplication and division in various formats, adding and multiplying fractions, finding equivalent fractions for repeating decimals as well as using the “educated guess and check” method for computing square roots.  I may also dust off my knowledge of square roots by hand and share this division-related topic.

So how would you do 1472 divided by 5?  If you answered “With a calculator.”, you may find that most efficient but doing it by hand can help build estimation and computational skills while promoting Math facts and self-reliance.  In a tech-filled world, it can be wonderful to think independently without a calculator or Siri or Alexa or Google Assistant etc.

So sharpen your pencils and try my 3 favorite division problems on paper — yes please write these down and then close your laptop and/or power down your phone til it’s just you and the Math:

70 divided by 5
365 divided by 7
1000 divided by 8.