Q. A dealer allows a discount of 10% and still gains 5%. What % above the cost price must he mark his goods?

a)15%

b)20%

c)16 2/3 %

d)50%

Hot to go about this sum?

90SP/100 = 9SP/10= Marked Price

(9SP/10 - CP)/CP = 5/100=1/20

9SP/10 - CP = CP/20

9SP/10 = CP/20 + CP=21CP/20

SP = (21CP x 10)/(20 x 9)=7CP/(2 x 3)=7CP/6

SP = 7CP/6

Okay....I'm getting muddled after this.....