Mean of Means

If $a_i,b_i$ are positive numbers for $i=1,\cdots,n$, and

$! M_r (a,b) = \left( \frac{a^r+b^r}{2} \right)^\frac{1}{r}$

Prove that for $0 < r < s$,

$! \displaystyle \sum M_r(a_i,b_i) \sum M_{-r}(a_i,b_i) \leq \sum M_s(a_i,b_i) \sum M_{-s}(a_i,b_i) \leq \sum a_i \sum b_i$