We made a down payment of $100 and borrowed the balance on a new piano which cost $1000. The balance with interest was paid in 23 monthly payments of $40 each and a final payment of $70. The amount of interest paid was what percent of the amount borrowed?  Select the correct option
A) 6% B) 7% C) 8% D) 9% E) 10%
We borrowed $900.   To pay back this loan, we paid 23*$40 + $70=$990.   The interest was $990-$90023* 40 +  70= 
<gadget id="calculator">23* 40 +  70</gadget>
<output>990</output>
$990.   The interest was $990-$900=$90.   The percentage was $90/$900990- 900= 
<gadget id="calculator">990- 900</gadget>
<output>90</output>
$90.   The percentage was $90/$900=0.1  90/ 900= 
<gadget id="calculator">  90/ 900</gadget>
<output>1/10 = around 0.1</output>
0.1=10%.   The answer is 10%.
<result>E</result>
We made a down payment of $100 and borrowed the balance on a new piano which cost $1000. The balance with interest was paid in 23 monthly payments of $40 each and a final payment of $70. The amount of interest paid was what percent of the amount borrowed?