No Frills MATHs Skills for Parents 4: FRACTIONS for Beginners

Here is a post on Lego Fractions by New York Grade 3 teacher Alycia Zimmerman. Surprisingly I found this on an art website.

Just play with the Lego blocks. Add and subtract … you can even multiply and divide.

Next time.

Trick 4: How to be a Mathematical Clairvoyant

How to be a Mathematical Clairvoyant

Requirements: Spooky music and spooky look.

You will find some spooky music here.

Tell your students you will beat them  adding up 5 x 5 digit numbers in your head when they are using calculators.

Method:

1. Ask a student to write down 2 x 5-digit numbers on the board.

2. You rapidly write a 5-digit number underneath.

3. Ask another student to write another 5-digit number.

4. You write another 5-digit number quickly.

5. You have 5 by 5 digit numbers. Say ‘Go’. You instantly write down the answer.

Stand back.

This is how it works:

N₁ = 97413

N₂ = 28619

N₃ = 71380  (Each digit in N₃ that you write down must add up to 9 with digits in No. above)

N₄ = 64231

N₅ = 35768  (Once again each digit in N₅ must add up to 9 with digits above)

Now you will instantly write down the sum of these five numbers as

297411

Da! DA!

The trick is to subtract 2 from N₁ and put it in front:

N₁ = 97413

N₁ -2 = 97411

Sum of 5 numbers = 297411

This is why it works:

Hint: When you get your students to add up the five 5-digit numbers on a calculator you will beat them, but they will also get many different answers as a number of students will key incorrect numbers.

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