A machine is sold by A to B at a profit of 10% and then B sold it to C at a profit of 20%. If C paid ₹ 1200 for the machine, what amount was paid by A to purchase the machine?

Cost price of machine for C = Selling price of the machine for B = ₹ 1200

∴ SP = CP (1+P/100)

1200 = CP (1+20/100)

⇒1200=CP×120/100 

∴CP=(1200×100)/120=Rs 1000 

CP of machine for B = SP of machine for A = Rs 1000

SP=CP (1+P/100) 

1000=CP (1+10/100) 

⇒1000=CP×110/100

∴CP=(1000×100)/110=Rs 10000/11 

=Rs 909 10/11

Hence, the required cost price = ₹ 909 10/11 or ₹ 909.09 (approx)