How much juice concentrate must be added to a 15% juice to produce 2L of 25% concentrate juice?

Question

We vneed to increase the current concentration of juice from 15% to 25% and end up with 2L of juice.

Answer 1

Let J litres be the amount of concentrate added, then 2-J is the amount before adding it. 15% of this was concentrate, that is, 0.15(2-J) litres of concentrate. After adding, we have 2L of diluted juice and 25% of this is concentrate=0.25×2=0.5L.

Therefore 0.15(2-J)+J=0.5, 0.3-0.15J+J=0.5, 0.85J=0.2, J=0.2/0.85=4/17 or about 0.2353L of concentrate to be added.