Can every natural number be formed as the difference of two primes?
No! Most odd numbers can't, unless they happen to be 2 less than a prime number, as the difference between two prime numbers is even, unless one of them is 2.
I'm with reinout and zegroes on this. The forum might be a little "messy" but a much more structured look/feel would probably put off several who need help but would not ask for fear of being laughed at by "serious" mathematicians.
z=1.96 corresponds to a 95% confidence interval, and according to http://en.wikipedia.org/wiki/Margin_of_error this means the margin of error is approximately 0.98/√n
To see how to enter the degree symbol have a look at the answer here: http://web2.0calc.com/questions/how-to-enter-a-degrees-symbol#r1
Use the calculator on this site and type this in just as you have written it here; then press Enter.
If you save money in a bank, the bank uses Melody's method to decide how much to pay you back. If the bank loans you money it uses Chris's method to decide how much you must pay back.
No, ignore me; I'm just being cynical!!
The difference between Chris and Melody is just because of when they assume interest is added. See:
Rosala; hint: you have too many x2's and not enough x's
+33666 
