Ab The price ratio of the two commodities is 7:3. If their prices increase by 700 respectively and the price ratio is 7:4, then a commodity is original.
Suppose commodity A is 7x yuan and commodity B is 3x yuan.
(7x+700):(3x+700)=7:4
4(7x+700)=7(3x+700)
28x+2800=2 1x+4900
7x=2 100
x=300
7x=2 100
3x=900