# New to APCSP! Number system conversions?

For the AP exam, how much do the students have to know regarding number system conversions? Hexadecimal to binary to decimal (back and forth)? Octal? Do they have to add and subtract?

I have looked all over and cannot find this.

Thanks!!!

Hey @hcook if you want the authoritative answer you can check the CSP Course and Exam description from the College Board here. The short answer, however, is that students don’t need to be able to add or subtract binary numbers or understand octal. They do need to convert between decimal and binary and understand some basic properties of binary numbers (e.g. an extra bit doubles the total number of possible values).

Hope that helps a little!

Thanks!! Do they have to do conversions with hexadecimal?

Students are expected to know what hex is and be able to convert back and forth between hex and binary yes. While theoretically that’d mean they have to know how to convert between hex and decimal as well (hex --> binary --> decimal) that rarely comes up. It’s more important that students understand that hexadecimal is a shorthand for binary sequences. If you want to see how this is covered in the curriculum I recommend you check out Unit 2 of the course and in particular lesson 4.