>>99
(Σ[k=1, n] k^3)(Σ[k=1, n] k^4)
-------------------------------------------
(Σ[k=1, n] k^2)(Σ[k=1, n] k^5)

　((1/n)Σ[k=1, n] (k/n)^3)((1/n)Σ[k=1, n] (k/n)^4)
= ------------------------------------------------------------------------------
　((1/n)Σ[k=1, n] (k/n)^2)((1/n)Σ[k=1, n] (k/n)^5)

　 (∫[0, 1] x^3 dx)(∫[0, 1] x^4 dx)
→ ------------------------------------------
　 (∫[0, 1] x^2 dx)(∫[0, 1] x^5 dx)

= ((1/4)*(1/5))/((1/3)*(1/6)) = 9/10