A chemist has one solution containing 50 cid and a second one containing 25 cid. How much of each should be used to make 10 liters of a 40 cid solution?
(a) 2.5 liters of the first solution and 7.5 liters of the second solution
(b) 5 liters of the first solution and 5 liters of the second solution
(c) 7.5 liters of the first solution and 2.5 liters of the second solution
(d) 10 liters of the first solution and 0 liters of the second solution