A commodity is sold at 20% discount, still 10% is gained by selling it. Calculate the cost price of the article whose selling price is Rs. 220.
S.P. M.P. C.P.
80 100 (100110×80)
S.P. : C.P. :: S.P. : C.P.
80:(100110×80)=220:x
[Using method of proportion]
∴x=100110×80×22080
=Rs.200