Rosamaria is setting up a 20-gallon saltwater fish tank that needs to have a salt content of 3.5%. If Rosamaria has water that has 2.5% salt and water that has 3.7% salt, how many gallons of the water with 3.7% salt content should Rosamaria use?

1 Answer
May 24, 2017

$3.33$ gallons from 2.5% salty water and $16.67$ gallons from 3.7% salty water, well mix, that is done Rosamaria!

Explanation:

Your mathematical expression is:

$\left(0.025 \cdot x\right) + \left(0.037 \left(20 - x\right)\right) = 0.035 \cdot 20$

x stands for volume of water required from 2.5% salty water stock. When you get this amount, the rest (20-x) will be taken from 3.7% salty water stock.

Solve this question:

$0.025 \cdot x + 0.74 - 0.037 \cdot x = 0.70$

$0.74 - 0.70 = 0.012 \cdot x$

and x is

$x = \frac{0.04}{0.012} = 3.33$ gallons.

Take 3.33 gallons from 2.5% salty water stock and take $20 - 3.33 = 16.67$ gallons from 3.7% salty water stock. Mix your water. Rosamaria finally gets 3.5% salty water of 20 gallons total. Well done!