Question

A chemist needs 90 milimeters of a 71% solution but has only 67% and 76% solutions avaliable. How many milimeters of each that should be mixed to get the desired solution?

Answer 1

wow i did this exact same problem yesterday.
where does it come from?

Answer 2

a homework that I don't understand :(

Answer 3

Homework or test?

Answer 4

Make up Test

Answer 5

A chemist needs 90 milimeters of a 71% solution but has only 67% and 76%
90 milimeters of a 71% -> 90*71% gives us the amount of the solute (the "salt" in salt water)

Answer 6

if x and y are the amount of 67% and 76% we add, then
90*71%=67%*x+76%*y

Answer 7

get rid of the percents (multiply by 100)
90*71=67x+76y

Answer 8

and, x+y=90, because the total amount of solution (the seawater) will be 90 ml

Answer 9

no matter we can do it again. we need a variable so put
\(x\)= number of ml of 76% solution,
which will contribute \(.76x\)

since the total is 90 ml the amount of 67% solution will be \(90-x\)
and that will contribute \(.67(90-x)\) to the total.

since you want 90 ml of 71% solution the total is
\[.71\times 90=6.39\] and now we now have two expressions for the total so set them equal and solve
\[.76x+.67(90-x)=6.39\] for \(x\)

Answer 10

clear the decimals and get
\[76x+67(90-x)=639\] and go from there

Answer 11

oh, sorry
what inkyvoid said