If  a,   b,   c  are in A.P. and  a²,  b²,  c² are in G.P. such that
a < b < c and   a + b + c = $${3 \over 4},$$ then the value of a is :

If b is the first term of an infinite G.P. whose sum is five, then b lies in the interval :

If x₁, x₂, . . ., x_n and $${1 \over {{h_1}}}$$, $${1 \over {{h_2}}}$$, . . . , $${1 \over {{h_n}}}$$ are two A.P..s such that x₃ = h₂ = 8 and x₈ = h₇ = 20, then x₅.h₁₀ equals :

Let

S_n = $${1 \over {{1^3}}}$$$$ + {{1 + 2} \over {{1^3} + {2^3}}} + {{1 + 2 + 3} \over {{1^3} + {2^3} + {3^3}}} + ......... + {{1 + 2 + ....... + n} \over {{1^3} + {2^3} + ...... + {n^3}}}.$$

If 100 S_n = n, then n is equal to :