How many liters of a 40% iodine solution need to be mixed with 35 liters of a 20% iodine solution to create a 31% iodine solution?  Choose the most appropriate option:
A) 35 B) 42 C) 100 D) 105 E) 140
Solution 1:   Assume the iodine solution to be mixed = x lts.   Iodine = 0.4x lts, Water = 0.6x lts.   Solution 2: 35 liters of a 20% iodine solution   Iodine = 7 lts, Water = 28 lts.   Total iodine = 0.4x + 7   Total water = 0.6x + 28   The resultant is a 35% idoine solution.   Hence (0.4x + 7) / (x + 35) = 31/100   40x + 700 = 31x + 1085   9x = 385   x = 42 lts   Correct Option: 42
<result>B</result>
How many liters of a 40% iodine solution need to be mixed with 35 liters of a 20% iodine solution to create a 31% iodine solution?