What is the different between Lotrell 10/40 and Lotrell 10/20?

I currently have a perscription for Lotrell 10/40; however, I am out of capsules. I found 20 days worth of Lotrell 10/20 left over when my doctor was setting the correct dosage of Lotrell. Is is Ok to use this lower dosage for a week until my mail order perscription arrives?