discount, discount and discount...!

recently i went to a shopping mall at Penang.. there were many shop offer discount to customer coz hari raya will coming soon..in biz math discount given is called mark down..mark down is given to attract people to buy or the sellers want to clear the old stock and take new stock..sometimes the sellers will give up to 70% and sometimes they they will give a chain discount. chain discount is extra discount given to good that has been given a discount..for example 30%+20%..it always happen during festive season..when u saw this sign u think the discount given is 50% but u r wrong..the actual discount is less than 50%..if u want to know the real discount use this formula..1-(1-r)(1-r)..letter r the discount given after it is convert into 2 decimal place by divide it by 100..for example 1-(1-0.3)(1-0.2)..then u will get 0.44 and multiply it by 100 to get the real value that is 44%..the real discount given is actually only 44% not 50%..maybe this information is useful when u want to go to shopping in the future...adios..