Question

The class mark of a class is 25 and the class interval is 10.Find the class

Answer 1

Let the lower limit be x then upper limit = x+10.
Since, Class mark =(upper limit + lower
limit)/2
→ 25= (x+x+10 )2
→50-10=2x
→40=2x
→ x=20

Now , required class = x — x+10 = 20—20+10 =20-30

Answer 2

Here is your answer:
Let the upper class be x and lower class be y.
class mark = lower class + upper class ÷2
25= x+y÷2
25×2=x+y
50=x+y. (i)
upper class - lower class= class interval
x-y=10. (ii)
on adding (i) and (ii)
x+y=50
x-y=10
_____
2x = 60
x=30
substituting in equ.i
x+y= 50
30+y= 50
y=50-30
y=20

Therefore, class=20-30