Question

how much orange juice at 45 cents a liter should be mixed with grapefruit juice worth 35 cents a liter to make 200 liters of a mixture worth 40 cents a liter

Answer 1

To help you with the equation you should know that 40 is halfway between 35 and 45. That would mean that orange juice would make half of the mixture. It would also be the same for grapefruit juice. That would make it 100 liters of orange juice and grapefruit juice.