Putnam exam 2003

Questions to the 64rd annual Putnam exam:
Source: http://www.math.niu.edu/~rusin/problems-math/

       Questions from the 64th Putnam exam, Dec 6 2003.

A1
Let  n  be a fixed positive integer. How many ways are there to write  n
as a sum of positive integers,  n = a_1 + a_2 + ... + a_k,  with  k  an 
arbitrary positive integer and  a_1 \le a_2 \le .. a_k \le a_1  + 1?
For example, with n=4, there are four ways: 4, 2+2, 1+1+2, 1+1+1+1.

A2
Let a1, a2, ..., a_n  and  b1, b2, ..., b_n  be nonnegative real numbers.
Show that
      (a1 a2 ... a_n)^{1/n} + (b1 b2 ... b_n)^{1/n} <=
                       ( (a1+b1) (a2+b2) ... (a_n + b_n) )^{1/n}

A3
Find the minimum value of 
  | sin x + cos x + tan x + cot x + sec x + csc x |
for real numbers  x.

A4
Suppose that a,b,c,A,B= \int_0^1 |f(x)| dx.