In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $10 and the other one, that is cheaper, costs $3.5. The factory holds a $45 worth stock of 11 modules. How many of the modules in the stock are of the cheaper kind?
Choose the correct answer:
A) 30 B) 28 C) 25 D) 20 E) 10
So the number of $3.50 modules must be 10 so that the leftover 1 modules are of $10 which will give a total value $45. 10*3.50+1*10 = 35+10= 
<gadget id="calculator">35+10</gadget>
<output>45</output>
45   Answer : 10
<result>E</result>
In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $10 and the other one, that is cheaper, costs $3.5. The factory holds a $45 worth stock of 11 modules. How many of the modules in the stock are of the cheaper kind?