I would like to create a formula to multiply the data in A1 by a percentage
based on the percentage in B1. So, if B1<80% then A1x10%, if B1 is 80% to
89% then A1x15%, if B1is 90% to 99% then A1x18% and if B1100% then A1x20%.

Does anybody have a lot of experience with the if then function?