An alloy of tin is 15% tin and weighs 20 pounds. A second alloy is 10% tin. How many pounds of the second alloy must be added to the first to get a 12% mixture?
30 lb
40 lb
60 lb

Question

An alloy of tin is 15% tin and weighs 20 pounds. A second alloy is 10% tin. How many pounds of the second alloy must be added to the first to get a 12% mixture?
30 lb
40 lb
60 lb

anonymous · Answer

you have 20 pounds that is 15% tin so at the moment you have 15% of 20 is 3 pounds of tin. lets call the amount you add of the 10% alloy x
then if you add x pounds you will have $20+x$ pounds total, and the total amount of tin you have will be $3+.10x$ 
you want this to be 12% of the total, so put 
$$3+.10x=.12(20+x)$$ and solve for x

anonymous · Answer

can you solve this equation for x?

anonymous · Answer

30lbs

anonymous · Answer

yup