If {Σlimits_{i = 1}^{20} {left( {frac{{{}^{20}{C_{i - 1}}}}{{{}^{20}{Cᵢ} + {}^{20}{C_{i

English

Gujarati

Hindi

7.Binomial Theorem

hard

If ${\sum\limits_{i = 1}^{20} {\left( {\frac{{{}^{20}{C_{i - 1}}}}{{{}^{20}{C_i} + {}^{20}{C_{i - 1}}}}} \right)} ^3}\, = \frac{k}{{21}}$, then $k$ equals

$400$

$50$

$200$

$100$

(JEE MAIN-2019)

Solution

${\sum\limits_{i = 1}^{20} {\left( {\frac{{{\,^{20}}{C_{I – 1}}}}{{^{20}{C_1} + {\,^{20}}{C_{I – 1}}}}} \right)} ^3}$

Now $\frac{{^{20}{C_{I – 1}}}}{{^{20}{C_1} + {\,^{20}}{C_{I – 1}}}} = \frac{{^{20}{C_{I – 1}}}}{{^{20}{C_1}}} = \frac{1}{{21}}$

Let given sum be $S$, so

$S = \sum\limits_{I = 1}^{20} {\frac{{{{\left( i \right)}^3}}}{{{{21}^3}}}} = \frac{1}{{{{(21)}^3}}}{\left( {\frac{{20.21}}{2}} \right)^2} = \frac{{100}}{{21}}$

Given $S = \frac{k}{{21}} \Rightarrow k = 100$

Standard 11

Mathematics

Let $(1+2 x)^{20}=a_0+a_1 x+a_2 x^2+\ldots+a_{20} x^{20}$.Then $3 a_0+2 a_1+3 a_2+2 a_3+3 a_4+2 a_5+\ldots+2 a_{19}+3 a_{20}$ equals

normal

(KVPY-2009)

If $\sum_{ r =0}^{10}\left(\frac{10^{ r +1}-1}{10^{ r }}\right) \cdot{ }^{11} C _{ r +1}=\frac{\alpha^{11}-11^{11}}{10^{10}}$, then $\alpha$ is equal to :

hard

(JEE MAIN-2025)

If the sum of the coefficients in the expansion of ${(\alpha {x^2} – 2x + 1)^{35}}$ is equal to the sum of the coefficients in the expansion of ${(x – \alpha y)^{35}}$, then $\alpha $=

hard

The sum of the series $\left( {\begin{array}{{20}{c}}{20}\\0\end{array}} \right) – \left( {\begin{array}{{20}{c}}{20}\\1\end{array}} \right)$$+$$\left( {\begin{array}{{20}{c}}{20}\\2\end{array}} \right) – \left( {\begin{array}{{20}{c}}{20}\\3\end{array}} \right)$$+…..-……+$$\left( {\begin{array}{*{20}{c}}{20}\\{10}\end{array}} \right)$

hard

(AIEEE-2007)

If $r,k,p \in W,$ then $\sum\limits_{r + k + p = 10} {{}^{30}{C_r} \cdot {}^{20}{C_k} \cdot {}^{10}{C_p}} $ is equal to –

normal

If ${\sum\limits_{i = 1}^{20} {\left( {\frac{{{}^{20}{C_{i - 1}}}}{{{}^{20}{C_i} + {}^{20}{C_{i - 1}}}}} \right)} ^3}\, = \frac{k}{{21}}$, then $k$ equals

Solution

Similar Questions

Let $(1+2 x)^{20}=a_0+a_1 x+a_2 x^2+\ldots+a_{20} x^{20}$.Then $3 a_0+2 a_1+3 a_2+2 a_3+3 a_4+2 a_5+\ldots+2 a_{19}+3 a_{20}$ equals

If $\sum_{ r =0}^{10}\left(\frac{10^{ r +1}-1}{10^{ r }}\right) \cdot{ }^{11} C _{ r +1}=\frac{\alpha^{11}-11^{11}}{10^{10}}$, then $\alpha$ is equal to :

If the sum of the coefficients in the expansion of ${(\alpha {x^2} – 2x + 1)^{35}}$ is equal to the sum of the coefficients in the expansion of ${(x – \alpha y)^{35}}$, then $\alpha $=

If $r,k,p \in W,$ then $\sum\limits_{r + k + p = 10} {{}^{30}{C_r} \cdot {}^{20}{C_k} \cdot {}^{10}{C_p}} $ is equal to –

Start a Free Trial Now