In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $15 and the other one, that is cheaper, costs $10. The factory holds a $140 worth stock of 13 modules. How many of the modules in the stock are of the cheaper kind?	Pick one:
A) 20	B) 25	C) 30	D) 11	E) 35
So the number of $10 modules must be 11 so that the leftover 2 modules are of $15 which will give a total value $140. 11*10+2*15 = 110+30= 
<gadget id="calculator">110+30</gadget>
<output>140</output>
140   Answer : 11
<result>D</result>
In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $15 and the other one, that is cheaper, costs $10. The factory holds a $140 worth stock of 13 modules. How many of the modules in the stock are of the cheaper kind?