1.
Let $${{{b}}_{{i}}} > 1{\text{ for }} i = 1,2,....,101.$$ Suppose $${\log _e}{{{b}}_1},{\log _e}{{{b}}_2},.....,{\log _e}{{{b}}_{101}}$$ are in Arithmetic Progression (A.P.) with the common difference $${\log _e}2$$. Suppose $${{{a}}_1},{{{a}}_2},.....{{,}}{{{a}}_{101}}$$ are in A.P. such that $${{{a}}_1} = {{{b}}_1}$$ and $${{{a}}_{51}} = {{{b}}_{51}}$$ . If $${{t}} = {{{b}}_1} + {{{b}}_2} + ..... + {{{b}}_{51}}$$ and $${{s}} = {{{a}}_1} + {{{a}}_2} + ..... + {{{a}}_{51}},$$ then
A.
$${{s}} > t {\text{ and }}{{{a}}_{101}} > {{{b}}_{101}}$$
B.
$${{s}} > t {\text{ and }}{{{a}}_{101}} < {{{b}}_{101}}$$
C.
$${{s}} < t {\text{ and }}{{{a}}_{101}} > {{{b}}_{101}}$$
D.
$${{s}} < t {\text{ and }}{{{a}}_{101}} < {{{b}}_{101}}$$
Answer :
$${{s}} > t {\text{ and }}{{{a}}_{101}} < {{{b}}_{101}}$$
2.
Let $$x, y, z$$ be three positive prime numbers. The progression in which $$\sqrt x ,\sqrt y ,\sqrt z $$ can be three terms (not necessarily consecutive) is
If in A.P., $$\sqrt y = \sqrt x + \left( {n - 1} \right)d$$ and $$\sqrt z = \sqrt x + \left( {m - 1} \right)d$$
$$\therefore \,\,\frac{{\sqrt y - \sqrt x }}{{\sqrt z - \sqrt x }} = \frac{{n - 1}}{{m - 1}},$$ a rational number. As $$x, y, z$$ are prime, $$\frac{{\sqrt y - \sqrt x }}{{\sqrt z - \sqrt x }}$$ is irrational.
∴ irrational = rational (absurd). So, $$\sqrt x ,\sqrt y ,\sqrt z $$ are not in A.P.
Similarly, they are not in G.P. or H.P.
3.
In a, G.P. of $$3n$$ terms, $$S_1$$ denotes the sum of first $$n$$ terms, $$S_2$$ the sum of the second block of $$n$$ terms and $$S_3$$ the sum of last $$n$$ terms. Then $$S_1, S_2, S_3$$ are in
Let $$a$$ = first term of G.P. and $$r$$ = common ratio of G.P.;
Then G.P. is $$a,ar,a{r^2}$$
$$\eqalign{
& {\text{Given }}{S_\infty } = 20 \Rightarrow \frac{a}{{1 - r}} = 20 \cr
& \Rightarrow a = 20\left( {1 - r} \right)\,\,\,\,\,\,\,\,.....\left( {\text{i}} \right) \cr
& {\text{Also }}{a^2} + {a^2}{r^2} + {a^2}{r^4} + ..... + {\text{to}}\,\infty = 100 \cr
& \Rightarrow \,\,\frac{{{a^2}}}{{1 - {r^2}}} = 100 \cr
& \Rightarrow {a^2} = 100\left( {1 - r} \right)\left( {1 + r} \right)\,\,\,\,\,.....\left( {{\text{ii}}} \right) \cr
& {\text{From }}\left( {\text{i}} \right),{a^2} = 400{\left( {1 - r} \right)^2}; \cr
& {\text{From }}\left( {{\text{ii}}} \right),{\text{ we get 100}}\left( {1 - r} \right)\left( {1 + r} \right) = 400{\left( {1 - r} \right)^2} \cr
& \Rightarrow \,\,1 + r = 4 - 4r \cr
& \Rightarrow \,\,5r = 3 \cr
& \Rightarrow \,\,r = \frac{3}{5}. \cr} $$
6.
$$ABCD$$ is a square of lengths $$a,a \in N,a > 1.$$ Let $${L_1},{L_2},{L_3},.....$$ be points $$BC$$ such that $$B{L_1} = {L_1}{L_2} = {L_2}{L_3} = ..... = 1$$ and $${M_1},{M_2},{M_3},.....$$ be points on $$CD$$ such that $$C{M_1} = {M_1}{M_2} = {M_2}{M_3} = ..... = 1.$$ Then, $$\sum\limits_{n = 1}^{a - 1} {\left( {AL_n^2 + {L_n}M_n^2} \right)} $$ is equal to
A.
$$\frac{1}{2}a{\left( {a - 1} \right)^2}$$
B.
$$\frac{1}{2}a\left( {a - 1} \right)\left( {4a - 1} \right)$$
8.
Three positive numbers form an increasing G.P. If the middle term in this G.P. is doubled, the new numbers are in A.P. then the common ratio of the G.P. is:
9.
The fourth term of an A.P. is three times of the first term and the seventh term exceeds the twice of the third term by one, then the common difference of the progression is
Let the progression be $$a, a + d, a + 2d$$
Then $${x_4} = 3{x_1}$$
$$\eqalign{
& \Rightarrow a + 3d = 3a \cr
& \Rightarrow 3d = 2a\,\,\,\,\,.....\left( {\text{i}} \right) \cr
& {\text{Again, }}{x_7} = 2{x_3} + 1 \cr
& \Rightarrow a + 6d = 2\left( {a + 2d} \right) + 1 \cr
& \Rightarrow 2d = a + 1\,\,\,\,\,.....\left( {{\text{ii}}} \right) \cr} $$
Solving (i) and (ii) we get
$$a = 3, d = 2$$
10.
Let $$\alpha {\mkern 1mu} {\text{,}}{\mkern 1mu} \beta $$ be the roots of $${x^2} - x + p = 0\,$$ and $$\gamma ,\delta $$ be the roots of $${x^2} - 4x + q = 0.\,$$ If $$\alpha {\mkern 1mu} ,{\mkern 1mu} \beta {\mkern 1mu} ,{\mkern 1mu} \gamma ,{\mkern 1mu} \delta $$ are in G.P., then the integral values of $$p$$ and $$q$$ respectively, are