Question
The value of $$\left( {^{10}{C_0}} \right) + \left( {^{10}{C_0} + {\,^{10}}{C_1}} \right) + \left( {^{10}{C_0} + {\,^{10}}{C_1} + {\,^{10}}{C_2}} \right) + ..... + \left( {^{10}{C_0} + {\,^{10}}{C_1} + {\,^{10}}{C_2} + ..... + {\,^{10}}{C_9}} \right){\text{is}}$$
A.
$${2^{10}}$$
B.
$$10 \cdot {2^9}$$
C.
$$10 \cdot {2^{10}}$$
D.
None of these
Answer :
$$10 \cdot {2^9}$$
Solution :
$$\eqalign{
& \left( {^{10}{C_0}} \right) + \left( {^{10}{C_0} + {\,^{10}}{C_1}} \right) + \left( {^{10}{C_0} + {\,^{10}}{C_1} + {\,^{10}}{C_2}} \right) + ..... + \left( {^{10}{C_0} + {\,^{10}}{C_1} + {\,^{10}}{C_2} + ..... + {\,^{10}}{C_9}} \right) \cr
& = \,10 {\,^{10}}{C_0} + 9 {\,^{10}}{C_1} + 8 {\,^{10}}{C_2} + ..... + {\,^{10}}{C_9} \cr
& = {\,^{10}}{C_1} + 2{\,^{10}}{C_2} + 3{\,^{10}}{C_3} + ..... + 10{\,^{10}}{C_{10}} \cr
& = \,\sum\limits_{r = 1}^{10} {r{\,^{10}}} {C_r} = 10\sum\limits_{r = 1}^{10} {^9} {C_{r - 1}} = 10 \cdot {2^9} \cr} $$