Written question algebra last one i promise!! Please help

Question

You need a 70% alcohol solution. On hand you have 40 ml of a 35% alchohol mixture. You also have 75% alchohol mixture. How much of the 75% mixture will you need to add to obtain the desired solution? You will need _____ mL of the 75% solution to obtain _____ mL of the desired 70 % solution. 

Answer 1

Esme, same process.

 

Simultaneous equations.  Write first equation by using volumes - as in total = 40 + what you add.

 

Write second equation: 40(.35) + x(.75) = (40 + x)(.70)

 

Solve for x, which is the volume of 75% alcohol added.

Answer 2

Let x = volume of 75% sol'n to add

 

40*.35 + .75x = .70*(40 + x)

 

1400 + 75 x = 2800 + 70x

5x = 1400

x = 280

 

You should take this answer and plug into the origianl problem to make sure it is correct.