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4.Average
easy
The average height of the students of a class of $20$ is $105\, cm$. If ten more students of average height of $120 \,cm$ join this class, the average height of the class will become (in $cm$)
A
$115.7$
B
$115$
C
$110$
D
$112.5$
Solution
Average height of $20$ students in a class $=105 cm$.
After joining $10$ students of average height $120 cm ,$ average height of students of the class
$=\frac{20 \times 105+10 \times 120}{30}=2 \times 35+10 \times 4=70+40=110 \,cm$
Standard 13
Quantitative Aptitude