In assembling a Bluetooth device, a factory uses one of two kinds of modules. One module costs $6.25 and the other one, that is cheaper, costs $2.50. The factory holds a $70 worth stock of 22 modules. How many of the modules in the stock are of the cheaper kind?
It is easy go : consider x is count of costlier module. y is count of cheaper module.
6.25*x + 2.5*y = 70;
x+y = 22;
by solving these two equation we get y = 18
+1 Kudos if you like and understand.