Five amazing facts in mathematics

1. (6 × 9) + (6 + 9) = 69

2. The most popular favourite number is 7.

         (Nearly 3000 people, around 10% of the total asked, chose 7 as their favourite number in an online poll by Alex Bellos. The second most popular was 3.)

3. 0 .999999... = 1

         (If 10N = 9.9999...

Then N = .9999....

Subtract N from 10N, leaving you with 9N=9.

So then N=1. But we already know that N=.9999... as well.

So 1=.9999....)

4. 10! seconds is exactly 6 weeks.

         (10! means 10 factorial. 10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 3628800 seconds. Which is 42 days, or 6 weeks, exactly.)

5.A pizza that has radius "z" and height "a" has volume Pi × z × z × a.

          [Because the area of a circle is Pi multiplied by the radius squared (which can be written out as Pi × z × z). Then you multiply by the height to get the total volume.]