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4.Average
hard
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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