Question 168789
100-40=60%
100-30=70%
100-10=90%

in decimal form these are .6,.7,and .9 respectively

let x be the original cost

multiply these together .6(.7)(.9)x=.378x {{{37.8}}}% of x is the new cost of the item. 
:
In order to get the discount percentage you must 
take 100% and subtract out the new cost %(37.8%)={{{62.2}}}% or{{{.622}}}