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?

Question

anonymous · Answer

if you put $x$ as the number of gallons of 3.7% solution then you know the number of gallons of 2.5% solution must be $20-x$

anonymous · Answer

the $x$ gallons contains $0.37x$ salt, and the $20-x$ gallons of 2.5% solution contains $.025(20-x)$ salt

anonymous · Answer

you want that total to be $3.5\%$ of $20$ which is $.7$ so set 
$$.037x+.025(20-x)=.7$$ and solve for $x$

anonymous · Answer

probably easier to get rid of the annoying decimals by multiplying both sides by 1000 and start with 
$$37x+25(20-x)=700$$

anonymous · Answer

What is the answer

anonymous · Answer

i don't know, i didn't solve the equation

anonymous · Answer

X=0.12