This week's book giveaway is in the Big Data forum. We're giving away four copies of Elasticsearch in Action and have Radu Gheorghe & Matthew Lee Hinman on-line! See this thread for details.

Hi! A parking charge is 2 dollor for up to three houres. After 3 houres the charge increase with 0.5$ every houre. if a person parks his car 5.3 houres. He must pay 2$ for first 3 houres and 1.5 dollor for every houre 2+1.5=3.5$

because for 2 hourse we pay 1$ and for 0,3 houre we should pay 0.5 dollor more.

the above codes result is: 2+(0.5*(5.3-3))=3.15$ but it must be 3.5$ because for 2 houres 1$ and for 0.3 houre 0.5$ dollor more.

You need to round the number of hours up to the next half hour first.

If you already know this, (this was not clear in your question), and just want a suggestion on how to do it. I guess one trick is to double the value, round it up to the nearest whole number with the Math class, and half it back.