What is 15.99 with 10 percent off?

10% off means to calculate the 10%, then subtract from the original {or you could first say 100% - 10% = 90%, then multiply the original by 0.9 [for 90%]}.

Take the first one: 15.99 x 0.1 = 1.599, now subtract from 15.99 = 14.391, which rounds to 14.39