Question

The class-mark of the class 90-110_____

Answer 1

90+110/2
=200/2
=100
is the answer to ur question

Answer 2

Class interval = 90-110
Upper limit = 110
Lower limit = 90

Therefore,
$class \: mark \: = \frac{upper \: limit \: + \: lower \: limit}{2} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = \frac{110 + 90}{2} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = \frac{200}{2} \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 100$

Hope it'll help... :-)