Amdon and his decimal point

It was the arithmetic class and the teacher announced that she is going to teach about decimal points that day. Also, she said that the students who come for her tuition class now have a good understanding of decimal points.

She spoke for a while and wrote on the blackboard 10.9 and asked the class where is the decimal point. Most of the class gave the correct reply by saying it is in between zero and nine. And the teacher was happy.

She suddenly took the duster and erased the decimal point and asked the class, where is the decimal point now?

Amdon raised his hand and was given the chance to answer.

"Teacher it is in the duster now"He answered.