- Let the M.P of the article be x.
- A discount of 30% was given on the M.P.
- So the selling price of the article (S.P) = M.P - Discount.
- Discount = 30% of x 
[tex] =  \frac{30}{100} x \\  =  \frac{3x}{10} [/tex]
- Now S.P. = M.P - Discount
- or, S.P. 
[tex] = x -  \frac{3x}{10}  \\  =    \frac{10x - 3x}{10}  \\  =  \frac{7x}{10} [/tex]
- The shopkeeper loses Rs 400.
- Loss = C.P - S.P
- or, C.P = Loss + S.P.
- or, C.P = [tex]400 +  \frac{7x}{10}  \\  =  \frac{4000 + 7x}{10} [/tex]
- Now if he allows 10% discount then the gain is Rs 200.
- Gain = S.P - C.P
- or, S.P =  Gain + C.P
- S.P = [tex]200 +  \frac{4000 + 7x}{10}  \\  =  \frac{6000 + 7x}{10} [/tex]
- Discount = 10 % of x [tex] =  \frac{10}{100} x \\  =  \frac{x}{10} [/tex]
- S.P. = M.P - Discount
- or, [tex] \frac{6000 + 7x}{10}  = x -  \frac{x}{10}  \\  =  >  \frac{6000 + 7x}{10}  =  \frac{9x}{10}  \\  =  > 6000 + 7x = 9x \\  =  > 9x - 7x = 6000 \\  =  > 2x = 6000 \\  =  > x = 3000[/tex]
- The M.P of the article is Rs 3000.
- C.P = [tex] \frac{4000 + 7x}{10} \\ =  \frac {4000+7(3000)}{10} \\ = \frac{4000+21000}{10} \\ = 2500[/tex]
- The cost price is Rs 2500.
Answers:
Rs. 3000, Rs. 2500
Hope you could understand.
If you have any query, feel free to ask.