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
$4$
✓
$3$
D
$2$

✓

Answer

Correct option: C.

$3$

$3\text{r}+\text{r}+3=15$
$\Rightarrow 4\text{r}+3=15$
$\Rightarrow 4\text{r}=12$
$\Rightarrow \text{r}=3$

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