Average of 30 numbers is 12 . average of first 20 of them is 11 and that of next 9 is 10 . last numb

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4.Average

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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

$50$

Solution

Sum of all $30$ Number $=30 \times 12=360$

The last Number $=360-(20 \times 11+9 \times 10)$

$=360-(220+90)=50$

Standard 13

Quantitative Aptitude

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