This is like one of those questions on tests that ask "if two trains travel in opposite directions..."
Assuming that at least 1/2 sprout and planting 2 seeds per cell/hole/pot, then save 20 seeds. There's no harm in saving more. Just make sure you dry them out correctly and that they are collected from very mature red peppers that have ripened on the plant. We usually wait til the end of the growing season and let some peppers ripen nice and well and then pick them and then dry the seeds.