doubt in learning curve theory-help

in ca final cost management, in padukas saravana prasath book,page 19.4,sum no3,i have doubt.....

question:a plane costs 1500 lacs to manufacture and exhibits an 85%learning curve .calculate the cost of each of the first five planes.

cost of first 5 planes:

answer : 1.            1500 lacs*1.000                        =          1500lacs

                 2              1500lacs*0.8500                      =          1275lacs

                 3               1500lacs*0.7730                     =          1159.5lacs

                 4                1500lacs*0.7230                    =          1084.5lacs  

                5                 1500lacs*0.6860                    =          1029lacs

my doubt is how did the numbers 1.000,.8500,.7730,.7230,.6860 come........how to get those numbers????if anyon eknows the answer..please explain in detail....