Divisibility Rules

A Math friend sent me info on divisibility rules. Figuring out if a number is divisible by 7 has a few steps -- 1. double the units (ones) digit
2. subtract it from the rest of the number
If the difference is divisible by 7, so is the original number.
Example:
343 -- take off the 3 and double it to 6
subtract 6 from the remaining numbers (34)
34 - 6 = 28 -- which is divisible by 7 -- therefore, 343 is divisble by 7.

Statistics and 'The Curve'

After using IQ as an example of a normally distributed data set, students wanted to clarify that the mean will not always be 100 and the standard deviation will not always be 15 -- ;)

We spoke about how the class average and standard deviation can greatly influence letter grades because how one does relative to everyone else is often how grades are determined. We used an example of

Student A: Test Grade 78 Class Average 69 Std Dev 5
Student B: Test Grade 86 Class Average 78 Std Dev 8

z score for A = (78-69)/5 = 1.8 A is 1.8 standard deviations above the mean
z score for B = (86-78)/8 = 1.625 B is 1.625 standard deviations above the mean

Therefore A did better than B relatively even though their actual numerical grade was less!

Boy, did I ever live by this in engineering school. Senior year, I got a 7 (3.5/50) on a Communications Systems Design exam that I actually studied for!!

TODOS CEO Lecture at Teachers College

Last night (Monday 2/26) was the Colloquim at TC -- as always, it was informative -- the CEO of TODOS Miriam Leira from UNC Charlotte spoke about Equity for All in Math. She had some great slides on the achievement gap and emphasized that all students need individual attention.