A pharmacist mixed some 10%-saline solution with some 15%-saline solution to obtain 100 mL of a 12%-saline solution. How much of the 10%-saline solution did the pharmacist use in the mixture?

A 60 mL
B 45 mL
C 40 mL
D 25 mL

Question

A pharmacist mixed some 10%-saline solution with some 15%-saline solution to obtain 100 mL of a 12%-saline solution. How much of the 10%-saline solution did the pharmacist use in the mixture?

A	60 mL
B	45 mL
C	40 mL
D	25 mL

anonymous · Answer

put $x$ = ml of 15% solutions and since the total is 100 the amount  of 10% solution is $100-x$ therere the total amount  of saline you have  is $.15x+.10(100-x)$ and you want this to be equal to 12% of 100 = 12 so solve 
$$.15x+.10(100-x)=12$$ for $x$

anonymous · Answer

maybe easier to solve 
$$15x+10(100-x)=1200$$ 
$$15x+1000-10x=1200$$
$$5x=200$$ etc

anonymous · Answer

the answer should be 60 ml...so how do I get it? in your solution the answer is 40 ml...