Question

Number of non negative integral solutions of $x_1+x_2+x_3+x_4=20$.

• A. ${}^{23}{C}_3$
• B. ${}^{24}{C}_4$
• C. ${}^{23}{C}_4$
• D. None of these

Answer 1

The correct option is A ${}^{23}{C}_3$

No.of non-negative integral solutions

$x_1+..+x_r=n$

is ${}^{n+1-1}{C}_{r-1}{=}^{20+4-1}{C}_{4-1}{=}^{23}{C}_3$