Question

7. The average age of 30 boys of a class is
equal to 14 yr. When the age of the class
teacher is included the average becomes
15 yr. The age of the class teacher is
(1) 40 yr
(2) 42 yr
(3) 48 yr
(4) 45 yr​

Answer 1

Answer:

45 years

Step-by-step explanation:

x1/30 = 14

x1 = 420

x2/31 = 15

x2 = 465

Age of teacher = x2-x1

= 465-420

Age of teacher = 45 years

Answer 2

AnswEr:

Option (D) is correct.

Step By Step Explanation:-

Total number of students = 30

Average age of Students = 14 years.

$\large\bold{\underline{\sf{\red{Now,\: According\:to\: Question}}}}$

If Age of the Class Teacher is added the Average becomes 15 years.

After Adding teacher Number of observation becomes 31.

Finding the Sum Ages of 30 boys:

Sum of n observations = Average of observation × No. of Observation

$:\implies\sf\: Sum\: of \:Age \:of \;30 \;boys = 14 \times\: 30$

$:\implies\small{\underline{\boxed{\sf{\red{Sum\:of\:Ages\:of\:30\:Boys\:=\:420}}}}}$

$\rule{150}2$

Now, Average of boys when class teacher is included

Average of boys with teacher × Total number of observation

$:\implies\sf\: 15 \times \: 31$

$:\implies\sf 465$

Now, Finding the Age of Teacher

Age of Students with Teacher - Age of Students

$:\implies\sf\: 465 - 420$

$:\implies\sf\large{\underline{\boxed{\sf{\blue{Age\: of \: Teacher\:=\:45\: years}}}}}$