Question

71
65. Average marks of 15 students of class first
is 160. Average marks of 10 students of
class second is 120. Average marks of 15
students of class third is 180. What will be
the average marks of students of all the
classes together?​

Answer 1

Answer:

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Step-by-step explanation:

$to \: find = \\ average \: marks \: of \: all \: students \\ (combined \: mean) \\ \\ given = \\ n1 = 15 \\ x1 = 160 \\ \\ n2 = 10 \\ x2 = 120 \\ \\ n3 = 15 \\ x3 = 180$

$so \: we \: know \: that \\ \\ combined \: mean = \frac{n1.x1 + n2.x2 + n3.x3}{n1 + n2 + n3} \\ \\ Xc = \frac{(15 \times 160) + (10 \times 120) + (15 \times 180)}{15 + 15 + 10} \\ \\ = \frac{15(160 + 180) + 1200}{40} \\ \\ = \frac{(15 \times 340) + 1200}{40} \\ \\ = \frac{5100 + 1200}{40} \\ \\ = \frac{6300}{40} \\ \\ Xc= 157.5$

$hence \: then \\ average \: marks \: of students \: of \: all \: the \: \\ </p><p>classes \: together \: is \: \: \\ 157.5 \: marks$