help me with this

Question

A chemist needs 80 milliliters of a 60% solution but she only has 58% and 66% solutions available. Calculate how many milliliters of each should be mixed to get the desired result. How many milliliters of the 58% solution should she use?

She should use
milliliters of 58% solution.

Answer 1

this is simultaneous equations with a bit of chem thrown in...

 

Let x = # of mL of 58% solution

 

Let y = # of mL of 66% solution.

 

x + y = 80mL, so, x = 80 - y

 

And, 

 

80 mL x 60% = (x mL x 58%) + (y mL x 66%0

 

substitute:

 

4800 = 58 (80 - y)  + 66y

 

4800 =  4640 - 58y + 66y

 

160 = 8y

 

y = 20 mL

 

x = 60 mL

 

Substitute back in to check.