CFAI Mock "2/10 net 40"

Q78 of AM session, why does this formula go to ^365/20 and not ^365/30? Isnt it 40 days minus 10? Thanks for any help.

Depends on which day the company is planning to pay the money back. If you’re calculating the cost assuming that pay back is on the 30th day, you would use 20 in the calculation. I haven’t taken the mock yet though.