Most Important Selected Qs for JEE AdvancedMathematicsPermutation and Combination
Coefficient of x^2 y^3 z^4 in the expansion of (x+y+z)^9 is equal to
Options
- AThe number of ways in which 9 things of which 2 alike of one kind, 3 alike of 2^ nd kind, and 4 alike of 3^ rd
- BThe number of ways in which 9 identical things can be distributed in 3 persons each receiving atleast two thin
- CThe number of ways in which 9 identical things can be distributed in 3 persons each receiving none one or more
- DThe number of ways in which 9 different books can be tied up in to three bundles one containing 2 , other 3 an
Correct answer
D. The number of ways in which 9 different books can be tied up in to three bundles one containing 2 , other 3 an
Step-by-step solution
Consider (x+y+z)^9= ^9 C_r x^ 9-r (y+z)^r= ^9 C_r x^ 9-r r^r C_p y^ r-p z^p[x+(y+z)]^9 put r =7 ; p =4 or ^9 C₂ ^7 C₃ ^4 C₄= 9! 2!3!4!