## Tuesday, February 10, 2015

### Five Things You Need to Know About Algebra, Part II

(Click on the comic if you can't see the full image.)

True story: a student exiting the bathroom after a Regents exam, spotted me in the hall and asked, ''Mr. Burke, what does an exclamation point mean in a math problem?'' It didn't help that it was a meaningless probably and nothing to do with statistics or probability.

On another note: the number 5040 is very interesting. Not only is it 7 X 6 X 5 X 4 X 3 X 2 X 1, but it is also 10 X 9 X 8 X 7 (and that also means that 10!/7! = 6!). But here's another interesting fact: If the Moon was sitting on Earth's equator, the distance from the center of the Moon to the center of the Earth would be 5,040 miles. Unfortunately, if the Moon were sitting on Earth equator, it would be very bad because we would all die. Food for thought.

Bill in Boston said...

"10!/7! = 6!"

You've actually shown

10!/6! = 7! = 5040

but divide by 7 and your claim is also true.

(And So 5040 = Perm(10,4) also, right?)

(x, why?) said...

Exactly!

My parenthetical expressions of thought are left as exercises for the reader.

10!/6! is 10 X 9 X 8 X 7, which I'd already written, so that was a little less interesting. But 10 X 9 x 8 = 6!, leaving 7 out of it altogether.

Guess I should always resolve my parentheses first!