9ines

A Student (okay, my son Sammy, who is a 7th grade student), gave me this math puzzle:

“Use 6ix (sic) nines to equal 100, you can use +, -, x, ÷, ( ). [No exponents]. 9, 9, 9, 9, 9, 9. Good Luck, Sammy”

Welp, I was stumped and had to have him give me an answer.

This was his solution:

(9 x 9 + 9) + (9 ÷ 9 + 9)

which equals

90 + 10 = 100


I brought the problem to some colleagues of mine, and here are their answers:

Dennis wrote:

(999 – 99) ÷ 9

which equals

900 ÷ 9 = 100


Greg wrote:

(9 ÷ 9 + 9) x (9 ÷ 9 + 9)

which equals

10 x 10 = 100


I don’t remember who gave me this one:

99 + (9 ÷ 9) x (9 ÷ 9)

which equals

99 + 1  x  1

which equals

99 + 1 = 100


I finally came up with my own solution:

(99 ÷ 99) + 99

which equals

1 + 99 = 100

 

I happen to like my solution, since it uses the same numbers each time (99). However, Dennis’s is lovely, since it goes from three digits (999) to two digits (99) to one digit (9).

Which do you think is the most beautiful solution? The one that uses the most operations, or the one that uses the fewest?

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Useful Information

compoFrom their youngest days, students will be exposed to a plethora of information, some good, some bad, some pointless.

And then there is information that is so important, so useful, that children are exposed to it all day, every day. Yet they never really notice.  I am refering to the Useful Information charts that appear on the backs or insides of composition notebooks.

Although most of the tables and charts show  math-related data —  Multiplication Tables, Metric Conversion Tables, etc., — there are some differences between charts and occasionally some truly obscure gold.

In this six-part series, I will compare different Useful Information charts and try to find unique features and otherwise uncommon nuggets of info.

SWAT

I just finished six weeks of SWAT — Students Will Ace Testing — in preparation for the New York State mathematics test. Everyday in one of two schools, working one-on-one with targeted students. We focused on particular math topics that were discovered to be the most common topics on the tests for the past five years. I hope the students that I worked with did well.

SWAT

SWAT T Shirt

December 2017
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