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 ?
"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 = 140 answer : d"
divide(subtract(140, 15), 10)