Tag: maths

Questions Related to maths

What is the geometric mean of $6$ and $24$ ?

  1. $10$

  2. $12$

  3. $14$

  4. $16$


Correct Option: B
Explanation:
Assume $a, b, c$ in G.P.
then $\dfrac{b}{a}=\dfrac{c}{b}$

$\Rightarrow b^2=ac$

$\Rightarrow b=\sqrt{ac}$

so, $G.M=\sqrt{ac}$

$=\sqrt{6\times 24}$

$G.M =12$

$a^x=b, b^y=c, c^z=a$
Find the value of x, y, z.

  1. $1$

  2. $Not$  $valid$

  3. $-1$

  4. $0$


Correct Option: A
Explanation:

${ a }^{ x }=b\ { b }^{ y }=c=>{ a }^{ xy }=c\ { c }^{ z }=a\ { c }^{ z }=a=>{ b }^{ yz }=a\ \left( { a }^{ x } \right) ^{ yz }=a\ { a }^{ xyz }=a\ xyz=1$

If there exists a geometric progression containing 27, 8 and 12 as three of its terms (not necessarily consecutive) then no. of progressions possible are

  1. $1$

  2. $2$

  3. infinite

  4. None of these


Correct Option: C
Explanation:
$8, 12, 29$

Let the first term be $8$

$\therefore a = 8$    ...(i)

Let the $p^{th}$ ther be $12$

$\therefore ar^{p-1} = 12$     ...(ii)

and $q^{th}$ term be $27$

$\therefore ar^{q-1} = 27$    ...(iii)

(i) / (ii)

$\dfrac{a}{ar^{p-1}} = \dfrac{8}{12}$

$\Rightarrow r^{p-1} = \dfrac{3}{2} = 1.5$      ...(iv)

(iii) / (i)

$r^{q-1} = \dfrac{27}{8} = \left(\dfrac{3}{2}\right)^3$

$r^{q-1} = (1.5)^3$    ...(v)

(v) / (iv)

$\Rightarrow \dfrac{r^{q-1}}{r^{p-1}} = \dfrac{(1.5)^3}{1.5}$

$\Rightarrow r^{q-1-p+1} = (1.5)^2$

$\Rightarrow r^{q-p} = (1.5)^2$

              $= (r^{p-1})^2$     ...from (iv)

$\Rightarrow r^{q-p} = r^{2p-2}$

$\therefore q-p = 2p-2$

$\Rightarrow \boxed{q=3p-2}$

for every distinct value of '$p$' there will be a district integer value of '$q$'

$\therefore $ Infinite no. of progression are possible.

option $C$