Question

The average marks of 7 students are 39 and
the average mark of 3 of them is 27. The aver-
age marks of the other four is
(a) 48
(b) 84
(c) 24
(d) None of these​

Answer 1

Given:-

• The average marks of 7 students are 39.

• The average mark of 3 of them is 27.

To Find:-

• The Average age mark of other four is.

Formulae used:-

• $\sf{ Average\:mark = \dfrac{Sum\:of\:the\:marks}{No.\:of\:marks}}$

Now,

→ $\sf{ Average\:mark =\dfrac{Sum\:of\:the\:marks}{No.\:of\: Students}}$

→ $\sf{ 39 = \dfrac{Sum\:of\:the\:marks}{7}}$

→ $\sf{ Sum\:of\:the\:marks = 39 * 7 }$

→ $\sf{ Sum\:of\:the\: marks = 273}$. ( x )

Hence, The Sum of marks of 7 Students is 273

Therefore,

→ → $\sf{ Average\:mark =\dfrac{Sum\:of\:the\:marks}{No.\:of\: Students}}$

→ $\sf{ 27 = \dfrac{Sum\:of\:the\:marks}{3}}$

→ $\sf{ Sum\:of\:the\:marks = 27 * 3 }$

→ $\sf{ Sum\:of\:the\: marks = 81}$ ( y )

Hence, The Sum of marks of 3 student is 81

So,

→ Sum of marks of 4 Student = x - y

→ Sum of marks of 4 Student = 273 - 81 → 192

Again,

→ $\sf{ Average\:mark =\dfrac{Sum\:of\:the\:marks}{No.\:of\: Students}}$

→ $\sf{ Average\:marks = \dfrac{192}{4}}$

→ $\sf{Average\:marks = 48}$

The Average of marks of 4 student is 48.