If ^15 C_ 3r = ^15 C_ r+3 , is then equal to: - Vidyadip

MCQ

If ${^\text{15}}\text{C}_{3\text{r}}={^\text{15}}\text{C}_{\text{r+3}},$ is then equal to:

A
5
B
4
C
3
D
2

✓

Answer

3

Solution:

$3\text{r}+\text{r}+3=15$

$\Rightarrow 4\text{r}+3=15$

$\Rightarrow 4\text{r}=12$

$\Rightarrow \text{r}=3$

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