Suppose you have a container filled with iron and sand. you can separate the iron from the sand if you so this is a a) use a magnet; mixture b) melt the sand; mixture c) add baking soda; chemical compound d) dissolve the sand in water; solution

Aresistor with an unknown resistance is connected in parallel to a 9 ω resistor. when both resistors are connected in parallel to an emf source of 21 v, the current through the unknown resistor is measured with an ammeter to be 4 a. what is the resistance of the unknown resistor? answer in units of ω.