So hmmm, first off, let us use the percentage in decimal format, so 20% is just 20/100 or 0.2 and so on
hmm thus
whatever the amounts of "x" and "y" are, we know they have to add up to 30Litres, thus x + y = 30
and we also know the concentrated amount of pineapple, have to also add up to 7.5 thus 0.2x + 0.4y = 7.5
thus
solve for "x", to see how much of the 20% pure juice will be used
what about "y"? well, y = 30 - x
hmm thus
whatever the amounts of "x" and "y" are, we know they have to add up to 30Litres, thus x + y = 30
and we also know the concentrated amount of pineapple, have to also add up to 7.5 thus 0.2x + 0.4y = 7.5
thus
solve for "x", to see how much of the 20% pure juice will be used
what about "y"? well, y = 30 - x