Out of four numbers average of first three is 16 and that of last three is 15 . If last number is 20

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4.Average

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Out of four numbers the average of the first three is $16$ and that of the last three is $15 .$ If the last number is $20$ then the first number is

A

$21$

B

$23$

C

$28$

D

$25$

Solution

Let the $4$ numbers be $a, b, c, d$.

Average of $a, b, c=16$

$a+b+c=48$

Average of $b, c, d=15$

$b+c+d=45$

$(a+b+c)-(b+c+d)=48-45$

$a-d=3$

$a-20=3$

$a=23$

Standard 13

Quantitative Aptitude

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