Shatish sold a music system to Karan at a 25% gain and Karan sold it to Swati at a 30% gain. If Swati paid Rs. 12,500 for the music system, what amount did Shatish pay for the same?

Let the cost price for Shatish be Rs. X.
Shatish sells to Karan at a 25% gain, so selling price for Shatish (Cost price for Karan):

CP
Karan
​
=X×(1+
100
25
​
)=X×
100
125
​

Karan sells it to Swati at a 30% gain, so price paid by Swati is:

Price
Swati
​
=CP
Karan
​
×(1+
100
30
​
)
12500=X×
100
125
​
×
100
130
​

Solving for X:

12500=X×
4
5
​
×
10
13
​

12500=X×
40
65
​

X=
65
12500×40
​

X=
65
500000
​
≈Rs. 7,692.31