The $average$ of $30$ numbers is $12 .$ The $average$ of the first $20$ of them is $11$ and that of the next $9$ is $10 .$ The last number is
The $average$ of $30$ numbers is $12 .$ The $average$ of the first $20$ of them is $11$ and that of the next $9$ is $10 .$ The last number is
- A
$60$
- B
$45$
- C
$40$
- D
$50$
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